How can I tell what version of an LP is best ?

Very well stated by Moonglum. But I must say, that like different cartridges, tonearms, preamps/amps, speakers and cables, it's what oooos and aaaahs *YOUR* ears that will tell the story. Personally, I almost always prefer the sound of original pressings over the reissues. While there are those who latch onto the dynamics and clarity of the latter I usually find the former easier and more traditionally "tube like" on my aging ears---and frankly, more natural sounding too. So, prepare for a return to those "thrilling days of yesteryear". Happy hunting and good listening!

Agree with the above and will add that Gemm.com is a good source for prices.

Steve Hoffman Forum (http://stevehoffman.tv/forums/) is my go-to forum for finding out about various pressings. A big community of obsessive vinyl fans over there. Fremer's Analog Planet is another good place to look, as is My Vinyl Review (http://myvinylreview.blogspot.com/) (though it is less frequently updated).

Amusing the drone on forums and audio rags of the vinyl/analog superiority and disparaging of CD medium. Jolly too the backslapping of support elicited and received from that modest bunch. Well done! Go team go, we're #1 rah rah.