Keith,
I think you'll find this site a treasurehouse of info. The folks here are GREAT!
I don't own one (YET!), but have been learnt a bit here.
Thunder Ranch Spyders are built on the Beck frame, and T.R. is the only "major" house which sells kits to be built. Both the Beck and Vintage are now solely turnkey now, so if you want to get your hands dirty, the T.R. is the way to go. If not, then since the TR and Beck are virtually the same it is a matter of wait-time and/or locale, as both are very good quality. Vintage has a different frame, providing rear suspension alternatives, and from I can gather is a premier builder also.
Tom McBurnie (of T.R.) is VERY reputable and knows his stuff. You can check with the San Diego Chapter of the PCA (Porsche Club) as many of the folks there are familiar with him and his work (their Monthly magazine "Windblown Witness" did a write-up of his RSK a couple years ago with race reviews).
Search the forums for a couple weeks and you'll find some very helpful info. A few personal, flaming "discussions" as to which is better (along with some fab comedy!), but I think most will come to the same bottom-line... beauty is in the eye of the beholder, just settle on the one YOU like best: it's your money, and YOUR car.
Welcome to world of the Spyder