I think the Real Tube Reverb is all tube, there are two 12AX7's in there.
The biggest difference between the Real Tube Reverb and the Valverb is both have gain and tone controls to help shape the reverb's sound; on the Valverb, the tone controls effect only the sound of the reverb itself which is pretty subtle, on the Real Tube Reverb, it affects your guitar's sound as well. This is much more effective for shaping the reverb sound when you are running the Real
Tube 100% wet in an effects loop, which is how I use it with the M4.
But the Valverb's tremolo is nice to have, too. Be careful of a used Valverb because some of them have problems with a volume drop using the tremolo, and spring crashing when you rack mount them, there's some mods to help both cases.
I liked both units, but give the edge to the Real Tube because of the second channel, you can string the two together for a really deep reverb, or use and set them independently of each other, which has interesting possibilities for guitarists as well.
A Real Tube Reverb went for more than $800 on eBay a couple months back, and I've seen Valverbs approach $300. $175 for a Valverb is a steal, assuming it works correctly. I picked up my Real Tube Reverb for $350 and was happy to pay it. I keep the Holy Grail as a backup.