That is an easy one. Not becasue it 'destroys' all the competition (lot of great amps listed in this thread.) But the Vitus house sound is something special.
The Vitus SIA-025 Mk2 or 030 if you needed a bit more power but don't let the power rating of either fool you. These are high current amps with 1.4kv trannies.
The only integrated amps I have not owned in this thread are any of the Hagel's, the 866 or the Dart. but on the other side of the pond, Vitus is king........8-10 mo production wait, nearly no product here in the USA. Rarely come up used, rarely come up in discussion.