Uncle,
I would probably agree with TT on this one. I used an old MNav for years and friends at contests would laugh at the knobs and switches on my computer but I loved the thing and found it easy to use and very accurate. I recently purchased a ship with a dated (But very functional) panel which included a Volkslogger and SN10. Problems started when one of the cables went bad and a new cable cost about half what the VL was worth. I decided to switch GPS sources to a PowerFlarm and discovered the SN10 would need another expensive cable and switch because it does not play well with devices other than the obsolete VL. After some head scratching I decided to go with a modern Vario and yank the old system. Here is what I have noticed; The new varios are much more configurable and tend to be more accurate and easier to use. I have the SC/Climb switch connected to the flap handle with a change in tone with a prescribed AS so I never have to look at the instrument to know which mode it is in. I am still fiddling but I cruise with it in Netto. The user interface is vastly improved and I have a fraction of the heads down time. Had I not installed the PF I might have kept the old Vario/Computer but I am glad I made the update.
To answer your question, Check the various manufacturer sites (LX Nav, Butterfly, etc) and Remde has a vario comparison page at Cumulus.
Best of luck.