I had the 2/95 and was looking to get the 2:90 just to shrink the overall size of my rig, but never had the cash or the need, so I opted for the 20/20. The 20/20 is a very loud power amp in a bedroom, if you're pushing it above 50% drive, your ears will be ringing. The 2/95 was obscenely loud and I rarely had it over 4 at show levels.
The main things are the 20/20 has EL84s in the output section which I like the sound of, you can push them hard faster to get that output tube drive at a lower overall volume. The 2:90 has some cool features such as the simulclass, modern, and deep modes for bass response and overall stiffening of the power supply to keep up with the demands placed upon it.
If you play large venues, you'll benefit from the 2:90, but if you're just playing bedroom and small clubs, the 20/20 will suit you just fine. there is also the 50/50 which is pretty nice as well. One bonus of the 20 is the space needed, single rack and not too heavy, plus retubing is WAY cheap compared to a 2:90 4x EL84's cost less in a matched set than 8x 6l6's.
Demo 'em and see what suits you.
You can find the 20:20 for under 400 used on eBay or http://www.Harmony-central.com
Let us know what you get and how you like it.