I'm a long time Thiel fan - I own old Thiel 02 speakers, owned the Thiel CS6, then later the 3.7 and the 2.7.
Been a long while since I heard the 3.6s but I have a decent memory of the sound.
Taste is subjective of course, but IMO Jim's last designs, re-designing the coax drivers, the woofers, drive motors, cabinets etc, further perfected his designs.
In the old designs I found that they certainly clicked at a precise listening position, but some slight diffraction and lobing effects could be heard with shifting of listener position (a common issue with first order designs).
Moving to the coax designs in the late 90's onward helped somewhat, and helped the speaker's coherence, but the issues still remained audible. Plus there was a slightly "reductive" quality, where instruments tended to sound a bit more squeezed down than on other speakers.(They were also slightly less bright sounding speakers).
The final design to my ear fixed all those issues. The coax design in the .7 series sounds smooth as silk, rich and utterly coherent from any position. In fact, top to bottom the 3.7s were the most coherent speaker I've probably ever heard, let alone owned (competing well with my old Quad ESL 63s).
So there was the super detail Thiel was known for, but more refined and organic, with just crazy imaging and soundstaging, and the tightes most tonally believable bass.
For me I'd pick the 3.7 in a heartbeat over the old 3.6.
But, since they do sound a bit different, taste comes in, and if you are used to one presentation you may prefer it. But the 3.7 to me is what Thiel was always shooting for - a more refined, coherent, natural sounding version of the "Thiel sound."