Most open venues have PA's, in which case either you'll need a wall of Marshall stacks, or you can do with a lower output amp and mic it to the PA.
Buy the Vox. From what I've heard, it's got a tube-based preamp stage. So unless you're gonna be pushing the output stage too hard (which won't be the case if oyu mic it), the Vox should sound close to all-tube amps. Btw, if you're mic'ing your amp, the lower the output the better, because you can get to sweeter overdrives without messing the stage volumes and troubling the sound tech with overloading his mics.
I'd say invest a bit and go for Vox AD15. Line 6 I've played - Personally, I find them to offer a lot of effects and brick-bracks, but not a good tone. Doesn't rock my boat. Marshalls MGs are the shits, but it again depends on what you're looking for.
IMHO, the best (and only) option is to go to a shop, and rock out on a few amps. Try out a few songs from your setlist on each amp, and see how the main rhythms, the leads, outros etc sound on each one of them. I usually find people hooking into one amp and playing SRV, then trying out another and playing EVH. That would not be a true comparison, unless you KNOW that the amp is voiced for a partiular tone.
'nuff said. Stop reading this, go out and rock on!
My gear, currently up for sale
Washburn X-16 anarchy - SOLD!!
duncan pickups - I wonder why Im selling these.