Bryston or McIntosh which would you buy?

I currently have a McIntosh MC752 amp, and am considering an upgrade in the future. I know the 752 is not one of McIntosh's best amps. I love mac gear as I always wanted to own their equipment.

1) How much of an improvement will I see going from the 752 to say a 7270 or similar?

2) How would it compare to something like a Bryston 4B?

Please note that there is a good chance I will upgrade my speakers...looking strongly at Thiel. Current preamp tube based Aronov.

Why not use both and bi-amp your speakers if they can accommodate them. That is what I have. The MC275 on the middle and top of my VR4JR speakers and the Bryston 4BST for the bass units with a McIntosh C2200 as preamp it is easy to set up. They match perfectly.
I would upgrade within the Mac line (Autoformer coupled) because I prefer the sound to Bryston, which is also good. In your case, I would stay with Mac especially since you are using Thiel speakers, which can tend to be bright, which Mac isn't and Bryston can be.
There has been quite a few Thiel,Bryston demoes at audio shows
Even James Tanner(Bryston) uses Thiel speakers(among others)
with 2XSS-2Thiel subs.I'd audition them at home if you can.
It does seem like Bryston and Thiel mate together very good.

I don’t know the 752, but I have owned the MC7270 (two of them at the same time), MC2255, MC352, and the MC402… The 7270 is a great amp but it is a bit dated, and was bested by the newer MC352 and MC402. That said, I ended up replacing the MC402 with a VTL ST-150, and never looked back. It was less than half the price of what I sold the MC 402 for, and sounded far better in my system (driving Dynaudio Special 25’s).

You may want to rethink solid state, altogether.
Find out what the shows are using for demoing. I actually went with Bryston $B-sst*2 because they all use it for Maggies and a LOt of Maggie owners say it is the amp to use or a Bryston 7bsst*2 pair
I am far more impressed with the Amp that=n the other Bryston stuff. i like the bryston/maggie with my old Audio Research Sp-15 the most..
Ran a pair of Thiel 2.3s off of a Bryston 4b-st for many years, with various preamps in front, both tubed and SS (VTL, Rogue, Plinius) -- and liked it plenty. Never compared with a McIntosh, though, so no use there. Still actually own all of it, but currently the Bryston is bridged and driving the center channel (also Thiel, and cetainly overkill) and the mains are all Rowland-fed. Bryston makes nice amps, and you can't argue with that warranty. Also not familiar with the 4b (compared to the -st and the yet more recent -sst), but word has it they've gotten more refined with each iteration. Often a fan of picking up stuff a generation or two older, particularly with amps, as you geat some great deals that way. A used -st seems to be going for less than half of used -sst gear. Yes, please.