I have a friend with the Theta ISP, he loves that, and it does sound really good.
Before this rig, I was always a rack guy. ADA preamps/power amps. But, they are getting older by the day and are subject to breakdowns....usually at a gig, never rehearsal. So, I had to update my stuff or deal with the issues of old gear.
I ended up getting a bargain modeler (didn't want to commit too much) and was running the ADA preamps for awhile, until my MP-2 started acting up. That was it, time to shop for another amp head.
My last head was a Hughes & Kettner Grandmeister deluxe 40. It was okay, I really gravitated towards the midi programmability. That was nice. Before that, I ran a Peavey Classic 20mh with a Boss MS-3. That was a sturdy rig for a long time before I got the H&K.
The Peavey taught me that 20 watts is plenty. In fact, I played a gig where I found myself really cranking the volume...which was unusual.....Turns out, I had the head set to 5 watts! I played the whole gig at 5 watts, with the amp almost dimed. haha - figured it out when I was tearing down.