I can't comment on 12AT7's because I never had a piece of gear that used them.
I have in my 12AX7 collection over 50 pairs of tubes from all the European and American companies. Famous Mullards, Amperex Bugle Boys, Telefunkens, Mazdas, etc.
If your piece can use 5751's I have found no tube that offers the sound of music better then these two: 1) Sylvania Gold Brand 5751's either gold or silver pins. 2) Mazda 5751 chrome plates.
They are not inexpensive, but not horrible expensive, and are so much better then even the highest regarded standard 12AX7's regardless the maker or time era. The Mazda's are very hard to get,but you should be able to score the Sylvania's. Remember not just Sylvania, but labed Sylvania Gold Brand 5751's.