Here is my $.02 after doing a few A/B comparisons over the past week:
VHT 2/50/2: awesome tone, power, and versatility, 2 channels, 2 rack spaces, about 32lbs., all tube, not cheap.
ART SLA-2: 95% as good as the VHT with the V7.0 poweramp sims, 2 channels, 1 rack space, about 20lbs., solid state, about $300 new.
Both units adequately power a 4x12 or 2 2x12's. If money, space, and weight are no object, I'd use with the VHT. Otherwise, I am really happy with the ART.
That being said, there are different opinions and I likely don't have as big of frame of reference as others on this board. Do a search on this site for the amps you are considering and you may get more information there.
All of this assumes you are going into a cab and not FRFR.