I have played the first few levels of Skull and Shackles a few times; the pirate archetype of Rogue was my favorite (as well as talking like Barbossa from Pirates of the Caribbean). I have been invited to a game with a new player to tabletop, but there will only be three players. I have also been asked to make sheets for the three of us.

What classes would you make for that adventure, since we will be a little short of power and the encounters will not change very much to compensate for that?

Class Restrictions: Only allowed Barbarian, Bard, Cleric, Druid, Fighter, Monk, Oracle, Paladin, Ranger, Rogue, Sorcerer, Swashbuckler, and Wizard

Race restrictions: Only allowed Dwarves, Elves, Gnomes, Half-elves, Half-orcs, Halflings, Humans

TL;DR: What classes should I choose to be powerful enough to run the four-man adventure path Skull and Shackles with only three PCs?

Cleric, druid, wizard. Power three.

My recommendation as a 3 man:

-Druid Shark Shaman or Storm Druid or Cleric
-Sea Witch
-Swashbuckler or Drunken Master Monk

AP are not super optimized...so the archetypes above, should be more than enough to survive the AP. The Monk or Swashbuckler is the front line, the Sea Witch brings arcane and the Druid shark shaman or storm druid brings the nature expertise and divine element spells that you need. If you want to be more flexible or versatile, you could technically switch the druid for a cleric, but cleric starts weaker at early levels.

Thanks, folks.

In my opinion if they are new you should start with easy classes. Fighter, Rogue and Barbarian are the easiest choices. (No casters because casters actually required moderately skilled players to be good.)

If the players are fairly quick on the uptake, Human/Elf Rogue, Human/Half-Orc Swashbuckler and Half-Elf/Halfling Bard. That covers 90% of almost everything you will face. Bard is your support and magic person with healing on the go, your rogue disables locks and helps you steal stuff like pirates do and your Swashbuckler keeps enemies at bay and is the rogues flank mate.

I can give you arrays and skills too depending on what your working with.

Yeah, don't play classes which are good only with skill, play classes which are never good!

OK, joking aside, there's nothing wrong with classes like Fighter (well, there is, but that's not the point) but you actually require more system mastery to play them well. A Cleric or Druid is a lot harder to mess up, even in Pathfinder (conversely, Pathfinder seems to be playing a cruel joke on new players - there are so many trap options for Fighter-types).

Also, new =/= stupid. Casters aren't exactly rocket science - I don't think I've ever not started with a caster in almost any game or system I've played. OK, memorising threw me for one back in Baldur's Gate but I never had anyone to explain it to me. Point is, you don't need to be a genius as long as you're happy to jump in at the (moderately) deep end (an appropriate analogy for Skulls and Shackles).

I'd probably suggest Witch over Wizard just because nabbing the Slumber hex gives you a powerful backup (or, hell, primary) option vs many types of foe, so it probably has a slightly higher optimisation "floor" (a Wizard played badly sucks as much as a Wizard played well dominates). Cleric and Druid are very solid, Sorcerer is a bit spells-dependent but pick decent picks and they're decent, Oracle too but they have a better chassis to fall back on.

If you want a simple character, I prefer Barbarian to the other martials. Grab a two-handed weapon (i.e. Greatsword - I guess a Lucerne Hammer works pretty well too), pump Strength, and just Rage and kill things. Just as simple to play, but harder to mess up building (even just do Power Attack at L1, Furious Focus at L5, maybe Vital Strike at L7 if you don't plan/expect to reach much higher levels or can retrain it - it's a naff feat but has a bit of a sweet spot around L6-7 and synergises with FF).

But really, it shouldn't matter that much - at L1, everyone's a single kobold arrow away from dying anyway (and in particular, the benefits of the more powerful caster classes like Wizard aren't fully realised) and it's not like the APs expect you to be optimised out the gunnels (more nautical metaphors!) or anything.

But seriously, Rogue is probably one of the worst classes for new people, there's no clear way to build them and in combat you're very reliant upon getting sneak attack to be useful which means flanking and stuff - way more tactical than a Barbarian (for example) and you're weak enough that it really matters that you do well at it. OK, you shine at skill checks, but that's about it.

In fact, something like this would probably work great:
Sorcerer - but pick some good spells out (probably Colour Spray, Enlarge Person, Ray of Enfeeblement, Grease, etc)
Witch - take Slumber (it's not just that it's common optimisation advice, it's also quite simple)
Cleric or Druid - Str-based, frontline melee but better at it than the actual melee classes

To be fair, the GM said he was building them and not the players. But building and playing a character are two entirely different beasts.

Also magus is a particularly better frontline melee. Particularly STR Tiefling Magus. Armor of the pit at 1st level and 14 dexterity means you have an AC of 18 (22 with shield) right out the gate. Thats only 2 points lower than a tower shield fighter at 1st level and lots of things cant hit you unless they roll a nat 20.

And its defensive options only get better with time. Mirror Image will carry you into the high teens and you can always refresh the spell by the time you get it and since your a STR magus and not a DEX magus, your AC gets really high if you spec into defensive options. Even with a d8 hit die, it wont really matter cause nothing can hit you and when it does it will miss 90% of the time.

If you have help building, a Sorcerer is not a bad choice at all, then - it's simple, and also effective. Most of the difficulty is in the spell picks.

Magus is great, but carrying a tower shield is one of the worst things you can do - you're not proficient so you suffer something like a -12 penalty to AB, and it causes a 50% chance of arcane spell failure. On a class designed around melee combat and arcane spellcasting... yeah, not great. Plus, you can't use Spell Combat with it! Any shield at all is basically a bad idea for a Magus.

I also don't really understand the rest of what you are saying. Str-based has worse AC than Dex-based, Tiefling is great and all but I'm not really seeing the synergy (you could easily just be a Tiefling Barbarian, for example) and Armour of the Pit is probably a decent pick at L1 but underwhelming thereafter (if you can retrain it I guess it's not an awful thing to take for starters). You basically seem to be saying that Mirror Image is good, which it is, but remember that Sorcerers and Wizards get it too.

The classic Shocking Grasp Magus or (my preferred) one which uses Frostbite is a pretty solid concept. I think it's slightly fiddlier than a Cleric or Druid, but it's plenty good enough.

Strength Magus has a higher AC value at endgame in terms of raw number. Sure a 18 dex with a chain shirt is really good at the start, but a strength Magus speced in Full-Plate will do better.

Strength Magus in full-plate: 14 AC with a max dex of 1, 3 in mithral.
Dex Magus may use studded Leather or normal leather but thats still only a +7/8 with a max dex of 8/7 depending on special materials used and armor type.

A dex magus in Leathers only have a max AC bonus of +15 where full-plate is two higher. Its not a huge diffrence, but being a strength magus means less rescources from things like feats bringing your damage online, which can be spent on better things like Improved Initative or Combat Reflexes.

Strength Magus main thing is that you are MAD for who your set up but you have more rescources for everything else in the long run. Dont need to burn 3 feats just to bring a dervish build online and you can wear the higher level armors that drop more frequently as you level.

Also Tower Shield fighter isnt the worst thing, especially if you do the fighter archtype. You dont lose any rescources aside from bonus to saves against fear, which goes to saves against area effects instead. Plus Tower Shield to touch AC turns you into the highest touch AC character present, unless you have a AC rogue being ran.

AC + Max Dex for armour is pretty consistently +8 to +10, which is your absolute cap. That's entirely dependent upon what armour you wear (assuming your Dex is high enough); there's nothing at all which stops a Dex-based Magus from wearing Full Plate. I don't really know why you would - you could wear a Mithral Agile Breastplate which is 1 AC lower but is much cheaper and lets you move at full speed. With a high enough Dex, you wear a Haramaki and beat armour entirely. Or, you're a Kensai. It doesn't really matter until the very high levels anyway.

Str-based certainly has big advantages, because Dex-based is hard in PF thanks to feat taxes and the fact that they apparently believe it to be super-overpowered for some reason (and then go and add Dex-to-damage options...). AC is not one of them.

As for the Tower Shield, I said it was an awful choice for a Magus. It so happens that it's a pretty awful choice for a Fighter, too - even the Tower Shield Specialist archetype (is that the one you mean?) doesn't add anything notable until L3 and still suffers the -2 to AB until L5! By then, you're giving up a lot of actually useful features to mitigate the massive penalties of a tower shield, so that you have have a net +2 to AC. Sure, at L1 a +4 to AC from a Tower Shield might make up for a -2 AB in a lot of cases, but I think I'd rather have a regular heavy shield (you're already giving up two-handed weapons) and anyway this will not age well. It seems like a slightly bizarre thing to mention, anyway.

Anyway, it's largely irrelevant for the purposes of this thread, since the OP has said that for some reason classes are restricted not to include the Magus. That's sad because the Magus is great, but you'll do fine with the options on offer.