Well, I'm not too picky and could be okay with missing any ride if the lines were too long. However, the ones I love the most and would rather not miss are the following...
MK - Peter Pan, Small World, and Pirates of the Caribbean. (I love lots of other rides at MK, but these are my top 3 that I would hate to miss.)
MGM - There's not much here that I am willing to wait in long lines for, but my favorites are Little Mermaid, Beauty and the Beast and Fantasmic...not really rides though.
AK - There are only 3 things here that DH and I care about doing normally anyway. The Safari, Dinosaur and Tarzan Rocks.
Epcot - Hmm...my favorites are Living with the Land (at least the way it was..who knows now??), El Rio del Tiempo and Maelstrom. Test Track is right up there too though.