We protect the Lords and the Lords protect the Crystal!
I'm going to assume Standard Array or Point Buy, since the infinite rerolls and Free Edit options makes most racial stat bonuses neglible. So my advice will assume a 27 point build with halfling racial bonuses in mind. You can use Free Edit to "change" where the racial bonuses go and still stick to a 27 point too, if that appeals.
Halflings lend themselves well to Dexterity based characters with a +2 bonus, so I'd probably begin with that. Island gets +1 Charisma and Marsh gets +1 Constitution.
Marsh are well suited for dex Fighters and Rangers, while Island can make very strong dex Paladins. All of these are good options for frontline characters. There are Strength boosting items available eventually and spells like Jump and Misty Step, so the less than ideal jump distance for dex builds won't be much of a problem with a bit of preparation.
You'll have to live with a max value of 15 at lvl 1 for Wisdom and Intelligence for the caster classes, which is a bit annoying, but it is still viable. Good play will compensate for that. For casters, both Clerics and Wizards are very strong. I recommend staying away from the Insight and Loremaster subclasses, but everything else is good. When Sorcerer is released, Island Halflings will make great use of that class.
Assuming a balanced party, you should probably have 1 warrior (fighter, ranger or paladin), 1 cleric and 1 wizard. That leaves 1 open slot, usually to reinforce one side of your party. Rogues are good skirmishers, a second warrior makes the party tankier and another caster can spiral out of control. If you want to play it safe, a Lowlife background warrior is a good option. They are more defensive than Rogues and the Lowlife background will let them pick locks.
Here is a party I could see working reasonably well:
Stats are displayed in this order: Str / Dex / Con / Int / Wis / Cha
Island Halfling Paladin. Rapier and shield for maximum AC. All subclasses are great. 12 / 16 / 14 / 8 / 10 / 16
Marsh Halfling Cleric. Oblivion, Battle, Law or Elemental Domain. 10 / 17 / 14 / 10 / 15 / 8
Marsh Halfling Wizard. Greenmage. 10 / 17 / 14 / 15 / 10 / 8
Marsh Halfling Ranger. Lowlife background. Hunter (Colossus Slayer, Multiattack Defense). 12 / 17 / 14 / 10 / 14 / 8
This party will be able to do a fair bit of damage at range, while also having staying power in melee. I recommend going for 18 dex and 16 int/wis for the wizard/cleric at level 4.