Your Favorite Class Feature?

[Ventnor]

Weapon and Armor Proficiencies.

[Anzyr]

False Channel. Accept no substitutes.

[Avoron]

In terms of game-breaking power, False Channel is definitely up there, although an optimized Elemental Eidolons still blows it out of the water.

[Sundakan]

Exploit Weakness is kind of a neat one. I just like the flavor of studying something, finding its weak spot, and just POUNDING it.

Good for characters who are into demolitions.

[Davor]

Honestly, I have to say Sneak Attack, and I'm going to echo what other posters have said. While there are a PLETHORA of powerful, super cool class features (The entire Thundercaller bard archetype gets a standing ovation from me), Sneak Attack is the perfect, simple class feature. It tells you what to do without giving you any finicky math, and encourages teamwork and cooperation to get the most out of your character.

[GeneMemeScene]

Originally it was Spellstrike, because flavor-wise it seems like what separates the gishes from the beefy wizards and self-buffing fighters. But then I played a Blade Adept Arcanist gestalted with a Swashbuckler.

Now it's Spell Combat, for mechanically allowing you to be an actual sword-and-magic blending warrior rather than a self-buffing fighter in some moments and an armor-wearing debuffer in others.

A weird mention goes to the Swashbuckler's Opportune Parry and Riposte. It's such a fun ability...but the fact that Paizo is so intent on making it "THE SWASH CLASS FEATURE" means that everyone else is locked out of it. Which is only made worse because I'm feeling more like the Swashbuckler never should have been its own class rather than just an archetype of the Fighter, and the general swashbuckling style should be open to far more classes.

[VRMH]

Lay On Hands.

A Cleric is a caster. A Paladin is HOLY.

[Rosc]

My favorite ability, by far, is the Summoner's Aspect ability, and Greater Aspect.

Aspect:

At 10th level, a summoner can divert up to 2 points from his eidolon’s evolution pool to add evolutions to himself. He cannot select any evolution that the eidolon could not possess, and he must be able to meet the requirements as well. He cannot select the ability increase evolution through this ability. Any points spent in this way are taken from the eidolon’s evolution pool (reducing the total number available to the eidolon). The summoner can change the evolutions he receives from these points any time he can change the eidolon’s evolutions.

Greater Aspect:

At 18th level, a summoner can divert more of his eidolon’s evolutions to himself. This ability functions as the aspect ability, but up to 6 evolution points can be taken. Unlike the aspect ability, the eidolon loses 1 point from its evolution pool for every 2 points (or fraction thereof) diverted to the summoner.

The Eidolon is a customization outsider buddy, but having the ability to slap some Evo points onto yourself is golden. 4 Natural Armor, an extra pair of limbs, wings, +8 racial to some skills, tremorsense, add some natural attacks, or more? And when Greater Aspect kicks in, you can become a g%@&!*n lava shark if you want to.

[Darigaaz the Igniter]

Rage
Judgement
Ranger's Focus

[Harleequin]

Ninja invisibility

[Helel13]

Spell Combat for sure. Effectiveness and optimization be damned, being able to fight and cast in a round is the dream of the "spellsword" class archetype lifers like myself

[Sir Charles the Bold]

Bardic performance. I've never had a situation where it isn't helpful

[Avadriel]

fast movement, because kiting is fun, and mobility is king.

[lareman]

Domains. Versatile, powerful and thematic.

[Wolfsnap]

Funky Fighter Feats. The fighter doesn't get nearly enough respect given all the cool stuff he can do.

[Dustyboy]

Anumal companion or familiar for me, just something about the role play value of having a creature that you're attached to which us likely also a huge liability ...

And In all honesty if your dm is letting you have a companion in town that isn't a horse or a dog without complaints from locals or the issues of independent feral animals and townsfolk then he's being too open minded