The cut to show your friend: I say either the theatrical cut or the supposive "Director's Cut" released by Warner (back before Scott did The Final Cut).
What to get: I recommend, if you can find it at a good deal, the Collector's Edition. Basically, you get 5 discs. That's all four versions of the film (theatrical, International Cut, Director's Cut and The Final Cut), a documentary, and some additional awesome stuff such as a 3D motion card, a replica of the origami unicorn, a small replica of the Spinner, and reproductions of the pre-production art, all in a small "Voight-Kampf" case, like seen below.