As always, the question is, "Which Star Trek, and which Star Wars?"
The first three Star Wars movies are pretty good to excellent. Big part of my life as a kid. The latest two movies don't merit mentioning. I've never gotten into the comics or novels.
Star Trek - the original series, hokey as it is, is a classic. The Movies run from excellent (II - Wrath of Khan) to abysmal (V - the Curse of Shatner). STNG started OK, built up to pretty darn good (especially after Ensign Evil Incarnate left). DS9, same deal. With Voyager, the franchise "jumped the shark".
But, what series will I actually shell out money for to get it on DVD?
Babylon 5.