I have 3 kinds - Schaller, PW, and Grover mini locking Rotomatics.
I like the Grovers the best. They're the kind that lock themselves as you start turning the peg. I find them to be the easiest to use and they work fine - no tuning issues with them at all.
The Schallers are good but it is possible to tighten the thumbscrew crooked. Not a big deal but it can be slightly annoying. Also the knurled knob hurts my tender fingers. :toothy10:
PW's are good, but I've heard that the cutting thing can screw up after a while. Also the thumbscrew can fall out if you loosen it too far. This can be slightly annoying but no big deal. Also, if you don't tighten them as hard as you can on the plain strings, there is a chance the string can pop out - and then you can never get it back in because the extra length is chopped off. Not a major problem, but it did happen to me once. I'm just extra careful to make sure it's good and tight.
All are good, but I like using the Grovers the best since I don't have to tighten anything down. Just pull the string through and start turning.