What can I say, I'm picky about controllers! I love the form factor of this thing. It's very pocketable and the perfect size for my phone (Motorola Photon Q). I just hate the analog sticks, loudness of buttons, and lack of L2 and R2 shoulder buttons. Thus begins a multi-part video series on improving it.
Before I got this thing, I used a USB PS2 controller clone with a clip I made to hold my phone. Very comfortable, but REALLY annoying to carry around. Also, the combination of the controller and running the emulators drained my battery pretty quick. Also used a wireless PS3 controller, which solved the battery drain, but not the portability problem.