I have two different types of locking tuners currently: Sperzels and Gotoh.
The Gotoh are great tuners. They turn well and the higher gear ratio makes for some finer tuning.
The Sperzels are solid locking tuners, but I'm not 100% satisfied. The lower gear ratio makes it difficult to get it "just right" with a strobe tuner. They look great, they have more mass than the Gotoh and they hold their tuning well, so those are all pluses.
I guess it comes down to gear ratio for me. A lower gear ratio will have more dramatic string movement. The Sperzels are capable of tuning dead on with a strobe tuner, but it may take a few times back and forth to get the right amount of string movement.
Planet Waves looks like an excellent alternative. The string cutting feature looks like a joke to me (cutting a string takes no time at all), but the higher gear ratio makes it look like it's very accurate.
I'd love to hear reviews of this thing:
http://www.stewmac.com/shop/Tuners/Guitar,_solid_peghead/Steinberger_Gearless_Tuners.html