Ive used the 306's and the 371's. Never had any problems with either of them. They work great. The 371's are the best in my opinion though. Lots of torque, fast, and they are see-through, so if you do ever lock one up, you can see whats wrong without having to take it out of the plane or disassemble it.

I have stripped a 306 in a crash. Even then it only broke one tooth.