Locking tuners are a Good Thing even if you don't
ever intend to use a vibrato bridge. It's easier/faster to get the string started properly, and easier/faster to get it off later. Plus, even without the winding/unwinding that happens with a wang bar, not having a several wraps on the peg means you don't suffer backlash as much, so detuning is more predictable, and when you tune back up it's more likely to stay where you put it. The whole thing is just a no-brainer.
As for which brand,
Sperzels seem to be the standard by which all others are judged. They've always made very high-quality, well-designed parts, and still do, for a reasonable amount of money.
Schaller locking minis are very much the same design, but they kick it up a notch by making the knurled nut you use to lock the thing a little bit thicker, so it's easier to get a grip on. They also have polished finishes, while the Sperzels are satin finished.
Planet Waves Auto-Trim tuners are again very much the same design, but they kick it up yet another notch by adding in an automatic string cutter in the post. After the string is locked and you're tightening it up to tune it, the excess string is cut off.
Planet Waves Auto-Trim tuners
I've used plenty of the Sperzels and Schallers, and can vouch for their quality and utility. Can't go wrong with them. I haven't tried the PWs yet, although I intend to. The design seems sound, with the locking method being proven and the cutting method being simple. My only concern is going to be how long that cutting edge lasts in real life. Cutting nickel-plated spring steel is tough on a cutting edge, so if they haven't taken measures to insure that edge is going to last those tuners could get to be a pain in the shorts. But, I haven't heard anything negative about that, so I may be worried about nothing. Thing is, they haven't been around long enough to gain any real empirical data on that issue.
Pretty much everything else is a compromise, and you don't want to do that with your tuners. I've seen guys get so pissed at guitars that wouldn't tune that they've smashed them into kindling. Nothing quite as frustrating as a guitar that fights tuning, or won't stay once you get it there. These three machines get the job done quickly, reliably, and hassle-free, then hold their place.
