The thing with preamp tubes is that they usually have a rated life of ~5K hours, which can lead to them being effectively ignored. They go south so gradually that you might not notice it until you swap in new tubes and then it's "holy crap!"
On the original question, I have more experience listening to ML than the others. Dad's system for 15 years was all-ML driving Wilson WP5s. No. 27, then a 27.5, then a 331 amp (which suffered from the cap failure and was repaired and fine thereafter), with 37 transport and 36 DAC, 38 pre (or was it a 38S?). Detailed and resolved, dynamic, yet also smooth and a tad polite (which was not incompatible with those Wilsons IMO). Downside to me was a sort of clinical sterility. I always thought a tube pre would have done wonders there, but Dad liked the all-ML system integration and aesthetics, and it's not like it sounded bad. ML amps of that era had high enough input impedance to work with most tube pres, not sure if that holds true of their more recent designs.
I now have the WP5s but none of the ML gear (system split up, divorce casualty). In shopping for amps I was looking at used gear. Would have grabbed a ML 334 if one came up in my time frame (didn't happen) because they're built like tanks and those tended to not have the capacitor failures. The large electrolytic caps they use are not ones you can just buy off the shelf in non-bulk quantity, and even though I've been building & fixing various electronics gear since before I had hair on my balls, they won't sell the caps to end users so you're looking at $4-figs for authorized service. Been a while since I heard one but the more recent 532H sounded very good and has supposedly been near bulletproof, but they're still not inexpensive on the used market.
You didn't ask, but I'll volunteer and not be offended if you ignore... I've become a big fan of Pass Labs. Nelson is generous with his time and advice, the amps are reliable but also easy to work on and source components for (mostly) should it become necessary. And most importantly, sound-wise, they generally tick the right boxes for me. A touch of warmth without being dark or veiled, all the bass slam and depth and resolution I need, lively without being too forward, just a nice balanced sound to my ears. Caveat for system matching is that they tend to have lower input impedances typical of most SS amps (20/30K), so you have to pay some minimal attention if you intend to pair them with a tube pre. Depending on the model, they can also throw off many more BTUs than ML or Bryston.
Bryston gear a few generations ago was somewhat harsh and not very detailed or resolving, but their recent stuff I've heard at shows (SST3) doesn't sound (on brief listening) like it has those faults. The 20-yr warranty is laudable.
Never spent extended time with ARC.
