I thought my Bel Canto REF1000s were the best bang for the buck. They were upgradeable from MkI to MkII specs which really really brought out the best of the sound.
I've since upgraded from the REF1000Ms to a pair of Electrocompaniet Nemos but I can tell you, the incremental improvement isn't a lot more than the difference in price tag would suggest.
I did find they could sound a bit lean and the depth of the soundstage wasn't as deep compared to more expensive amps but you could improve that with a good tube preamp. I have had great success pairing the Bel Cantos with Ayon CD5S (tube pre, CDP and DAC in one box) as well as an ARC Reference 5 (then 5SE).
I've since upgraded from the REF1000Ms to a pair of Electrocompaniet Nemos but I can tell you, the incremental improvement isn't a lot more than the difference in price tag would suggest.
I did find they could sound a bit lean and the depth of the soundstage wasn't as deep compared to more expensive amps but you could improve that with a good tube preamp. I have had great success pairing the Bel Cantos with Ayon CD5S (tube pre, CDP and DAC in one box) as well as an ARC Reference 5 (then 5SE).