Cold Steel Triad Lock
Every Cold Steel Voyager I've ever owned (until I messed one up by grinding the tang - and despite some play it is still strong). I've owned 3 XL Tantos, a Large Tanto, and a Large Clip point Voyager. All came rock solid. I don't own any Recon 1s any more, but I can't recall ever having any play in them either. My blue 4 inch Talwar also. The triad lock is hard to beat. I have a large Espada, and that one did actually have noticeable blade wiggle. Not visible, but I can feel it.
Spyderco Compression Lock
I have owned two compression lock knives, a Sliverax and a Mantra 3. For such a seemingly small amount of material in the locking mechanism, they are boss. No play at all.
Spyderco Caged Ball Bearing lock
I own two Manix 2 XLs with this lock, and they are devoid of blade play when the pivot is tightened enough to prevent a fidgety action. If I loosen the pivot some to allow a free swinging blade upon actuation of the lock switch, there is a minor side to side tick, but zero up and down.
Spyderco Liner Lock
The liner lock on the Spyderco value line is surprisingly sturdy as well, as proved to me by the Tenacious and two of the three Resiliences I have owned. I received one with a bit of noticeable play, and a visibly thinner lockbar. It was the exception, with some minor blade play that was an annoyance, but not a hindrance to safe function. Aside from that one, my other Resiliences even beat the Military for in hand lock strength. Something about the Millie I own makes the blade wiggle when I grip it tightly. It's an annoyance, but like my one Resilience, not a deal breaker. And when I don't touch the lock bar - near perfect lock up.
Ruike Liner Lock
I've only ever owned one knife, the P105-Q, and its liner lock is every bit as sturdy as my sturdiest Spyderco liner lock.
Spyderco Lockback
I've owned two Enduras, and my newest one (Wharncliffe) has very solid lock-up.
All in all, the best lock I own, or have ever owned, is a tie between the Triad lock on my Cold Steel Voyagers (and probably Recon 1s, but I can't remember for sure) and the compression lock on my Mantra 3 and now my friend's Sliverax.