Lately I've been using the Planet Waves tuners. 1:18 turning ratio, they cut the string off very nicely on their own saving you repeated risks on marring up your peghead with wire cutter marks (and one less tool you need to change a set of strings), they are lighter weight than most locking tuners and they have a cool black post that may look good with your overall color scheme.
That said, I have never been disappointed with the Schaller lockers either - built tough.
sperzel locking tuners. I've heard too many bad stories about planet waves tuners. sometimes they dont cut the string-excess, but the string itself. sperzels dont have that black peg itself by the way, which I think is but-ugly.
I like the Schallers best, but they are heavy and they only take up to a .060" string, which makes them just on the edge of insufficient for a seven-string guitar - those really need a .060" - .066" string for the low B. Some people dislike heavy tuners, but I personally think that more weight in the neck makes the guitar sound more even and sustain better. I have the Planet Waves on my seven-string, and they're OK too. The only thing I dislike about them is that the strings come off of them really high up the post, so you have to allow for that in your choice of string retainer or headstock design... you can wind the strings so that a few wraps of string lower that angle, but that's sort of antithetical* to the point of locking tuners. It really depends on your whammying requirements, and making a good nut, and everything else too.
I also like Planet Waves tuners. The only problem I've heard of is the cutter working on the wrong side of the string. But that always ends up being that people aren't paying attention to the orientation of little bump on the tuning post.
I have PW, Schaller/Fender locking and Grover minis. They all seem good to me. Certainly makes life a little easier. But so far nothing works as good as my old regular "made in West Germany" Schallers.
The PW's are my favorites so far with the locking type. I hope they hold up for a long time.
I've used the schallers and PW that Warmoth sells and also some too-expensive Gotoh ones from Stew mac. I'd say they are all pretty good, a lot depends on how you want it to look. I actually don't really care for the string-cutting mechanism, it cut off a b string once and then the string slipped out of the hole, and no way could I get it back in there with no play on it. Had to break open a new pack of strings. It takes about 20 seconds to cut off your string ends with snippers.
Schaller: simple and good but heavy
PW: works well overall, black / chrome can be ugly on some builds.
Gotoh 510 mini-locking: http://www.stewmac.com/shop/Tuners/Guitar,_solid_peghead_tuners/Gotoh_Mini_510_Locking_Tuners.html
Works as advertised, looks clean and vintagey, no thumbscrew, but the locking mechanism makes it a bit fiddly to get the string in the hole. Expensive.
If you're getting a locking nut, there's no need for locking tuners. Get the Gotoh sg 38 warmoth sells - cheap, high quality, good looking, simple.