I love fiddling around with character builds. Sometimes I come up with a concept and then try and find the most optimal way of achieving the concept and other times I start with a class and look at different ways it can be great.
Most of my current favorite builds are pretty conventional. The human Invulnerable Rager Beast Totem Superstitious barbarian that has an insane amount of HP, and uses Come and Get Me to counter attack enemies into bloody pulps. I tried this one but he died at level 4 when I rolled a 1 on a will save. Its a rather one dimensional character so I haven't had a lot of incentive to try him again
The Inquisitor is a class that I've been tweaking lately. I have two builds I like here. The Intimidator is a melee specialist that uses large weapons and Cornugan Smash to Intimidate his foes. I played this build at level 6 on a one shot adventure and it was quite fun. Lots of combat and non combat options but the build is a bit MAD and having only a moderate AC is a problem. With all of the Inquisitors set damage bonuses a Two Weapon build should be viable but they just don't get enough feats for it to be really effective.
The archer build works a bit better mechanically. Con is not quite so critical if you are not in the thick of things. Pathfinder archer builds tend to be ridiculously strong anyway and this build starts a little slow but will eventually outperform Ranger archers once high level inquisitor spells come into play. A round of buffing is required for the Inquisitor to be at its best. Multiclass in one level of rogue and you have a great rogue replacement with trapfinding.
The alchemist is an interesting class. It has rather diverse class features that don't really synergize but still complement each other. I've played around with strong melee builds, bomber builds, but then I started looking at a buffer/controller alchemist build. The idea here is to get you Int as high as possible and use the modified bombs to do knockdowns, stagger, or entangle. The DCs can get crazy high especially if you are using a Cognatogen (Mutagen variant). Because you can target different saves most of the time you can find the right tool for the job. Play a half orc for the extra bomb damage. You would have many more skills than a wizard, and good AE damage when you need it (with touch attacks so not likely to miss). The best part is the ability to hand out buffs using Infusions. You fighter buddy will love you when you hand him a Giant Form 1 Infusion he can drink just before a big battle.
I picture this character rather Beast like (the character from X-Men). He adventures in a lab coat, wears spectacles and he's a half-orc. He knows the answer to any knowledge question, buffs up his pals, and uses his bombs to entangle flying dragons, stagger opponents with multiple attacks, and knockdown enemy casters. Not a dominating character but useful in many different situations.
I tried to talk one of my players into playing something like this but they went rogue instead so that means that they now get to face him as an opponent. That is one advantage of being the DM, I get to throw of all my favorite character builds at the PCs and see how well they perform in combat. I think my 20th level archer Inquisitor will wipe the party but that encounter is still far far into the future. I expect the PCs to meet my first customized adventuring party sometime around Christmas. They need more time to mature as Dreadlords before I start throwing my optimized enemies at them.