Depends on who you ask. Build quality-wise they are like other amps in their price range. There is a Belaire in our church's youth room that is capable of some very nice tone.
They sound good. But I have a friend who owns 2 Nomads and a Belair. One of the Nomads is fine. The other 2 amps have intermittent noise issues which defy repeated attempts at repair. Not a great average.
Hasserl, then you might be interested in this. I put a straight Fender tone stack in my BelAir because I didn't like the way the Carvin was voiced, and then I made a big mistake; I traded the amp for a new ASAT Special. I think I'm going to buy another BelAir one of these days. I'm not kidding, it sounded absolutely great! And the conversion was really easy, you just take out the pots, put in the right values (Super Reverb stack), I think I had to cut a trace on the board, it's been a while...but it really made that amp sing. I'm missing it. The overdrive voicing and the cleans were both real nice.