For 15w a side, the 30RVS is louder than you'd think and using dual attenuators isn't practical.
It is handy though as a stereo effects return amp or you could run a preamp or dirty amp line out into one side and fx into the other, wet n' dry.
I bought the Gibson GA30RVS yesterday on ebay. In the review section of Harmon-Central reviewers say I can use a Ernie Ball volume pedal to turn the volume up to saturate the tubes and control the volume from the pedal, and plug a patch cord into one of the preamp outs to cut the amp into a 1X12 instead of stereo 2X12 for home practice levels. Will this hurt the amp? Also what company makes great EL84 tubes and are the tubes from former Soviet Bloc countries any good as replacements? They are very cheap compared to NOS.
They are fairly different amps. They both have fantastic clean sounds. The Gibson's clean is probably the best I've ever heard. The Supersonic has way more gain on tap. The Gibson will get you to ZZ Top country nicely, but that's about it. The SS has two independent channels rather than just the gain boost that the GA has, so it gives you much more control You could use a volume pedal in the loop to act as a master volume to control the overall level if you need to.
Of the two, I would have gone with the SS as it's way more flexible and sounds just as good, but it's too late now.
Played them both, owned the Gibson. Great sounding amp...when it worked. Double check the reliability of those before buying one. Mine had problems with the tube sockets and I read that several others did as well.