
Xarol Hopa |

I'd take a look at the Guide to the buffer bard. That is the most ludicrously effective assisting/buffing character I've yet seen in pathfinder.
https://docs.google.com/document/d/1b1hq_xhfCFjtAyjJMKrdtxRbtDEC1kNm6ZYfvS6 HqIw/edit?pli=1
If you're more interested in the aid another action specifically there are some prestige classes and class features that boost that, as well as some items. Combine those with bodyguard or some other way of generating actions and you can really help your allies.

Dragonflyer1243 |

This is an interesting build that you might like.
http://www.giantitp.com/forums/showthread.php?319607-PF-A-Brief-Guide-to-Ma rtial-Tanking
If not that, you can play a halfling bard and take all of the halfling feats that give bonuses to those around you when you fight defensively. This means that you're safe and your party is getting boosted both from your bardic performance and your feats.

Gwen Smith |

Halflings have some nice racial bonuses to helping other people:
1) The Helpful racial trait increases the bonus from aid another to +4.
2) The Cautious Fighter + Blundering Defense feat tree lets you give all adjacent allies a luck bonus to AC whenever you fight defensively (+2 minimum, bumpable to +3 in various ways) or take the total defense action (+3 to +4).
Any of the classes or archetypes that give teamwork feats make great helper builds: Cavalier, Fighter (Tactician), Paladin (Holy Tactician), Battle Herald...those are the ones I can think of off the top of my head.
My particular Helper build is a Halfling Honor Guard Cavalier:
(I used the Helpful racial trait and the Order of the Sword; if you don't use the Helpful trait, the Order of the Dragon is good)
Level 1: Unarmed fighter: Crane Style, Cautious Fighter
Level 2: Cavalier (Honor Guard), Mount Wolf (Bodyguard): Precise Strike (teamwork feat)
Level 3: Cavalier: Blundering Defense
Level 4: Cavalier: Bodyguard (bonus feat)
Level 5: Cavalier: Combat Reflexes
At this point, all adjacent allies get +3 bonus to AC, she uses Aid Another to add +4 to AC as an AoO, and she can designate a ward to get +1 dodge bonus during a challenge. Next series of feats might be Combat Expertise/Swift Aid or the Archon Style feat tree.
She is also getting the Benevolent enhancement on weapons and armor to increase the aid another bonus.