ST 70 best sounding version?

FYI: Bob Latino sells his wares on http://www.tubes4hifi.com/, along with Roy Mottram who sells pre-amp kits and customizations to original Dynaco 70s.

Regarding recitfer tube vs SS, Bob’s amp can run either without issue. In addition, there are a lot more upgrades to the amp beyond the power supply (output transformers, better caps, upgraded chokes, high precision resistors, driver circuit changes, a fully modern tube compliment, upgraded chassis, to name but a few). So IMHO Bob’s amps are really just modeled after the Dynaco ST70--his VTA 120 is a fully modern amp that is much closer to the Rouge Magnum and other modern tube amps that can run KT88s and KT120s (and now even includes an auto-bias board option.....)

Full disclosure--I own Bob’s VTA 120--super product with super support (something you might want to consider). Great supporting community as well.

 "....just not a 5AR4."  Noted :)

I have two Stereo 70s as well as Adcom 5802s and Sonic Frontier amplifiers. Both Stereo 70s have been updated. One has the original stock circuit with all caps and resistors replaced with modern polypropylene caps and metal film resistors. The updated stock amp sounds very nice. Sonically it has a lush midrange with a deep soundstage. The midrange is sweet sounding, bass is OK but not tight and the highs are pleasant.

The Curcio designed mod has both boards (4 6DJ8s). Sonically the amp is excellent, if the 6DJ8s are in good shape. The amp has a very open, clean sound, a deep and wide sound stage and tighter bass than the stock unit. Sonically it's not sweet sounding but seems accurate. 

The Adcom 5802s by comparison (bi-amped) are Nelson Pass designs (3 gain stages). The amps produce very tight bass, a wide and deep soundstage, very low noise, and a smooth and pleasant high end with excellent reproduction of spacial cues (when they exist). 

The Sonic Frontiers sound similar to the Curcio design with a bit more punch likely due to the larger power transformer and output transformers.