Spendor BCIIs, Rogers Monitor 2s and Studio 1s, many Mission 770s, and a slew of Canadian speakers (Energy, Image, etc.). I'm not saying that the Rega 3s are definitely the best. I love listening to them, keep coming back to them, and find them always musical and satisfying. I love Rega 2s as well, but the larger woofer and bigger cabinet elevates the 3s.
I love the Rega 3s aesthetically. The depth of the cabinet makes the proportions very elegant. The woofer mounted from inside and screw on rear baffle echo the British style. The construction quality is excellent (with extensive internal bracing), and the wood veneer is gorgeous.
I've been using these for more than 6 months (driven primarily by my Arcam Delta 60). They looked like a dog's breakfast until a few days ago, with scratches everywhere (including a couple of tic tac toe boards carved into one side), missing bottom trim pieces (where the brass badges would've been), and years of neglect. I refinished the cabinets (getting all scratches out:), applied new veneer at the bottom, and replaced the cheap speaker connectors with proper 5 way binding posts.
Most cool to me though, is that for the first time, I had Rega badges 3D printed! I've been following the development of 3D printing for a while now, and knew that there would be useful applications for a vintage freak like me. This was the ideal circumstance to try it out. Thanks to the nice people at 3DPhactory for their help.