I have favorites from both camps. If a show has memorable, recitable lyrics (anything by the Richard Stone team, as well as Bruce Broughton for Tiny Toons; Disney Afternoon shows), I'll enjoy that kind, but I won't turn my nose up at instrumentals, either. In fact, some of my favorite themes are lyric-less (Simpsons, Ren & Stimpy, Angry Beavers, Duckman, Cowboy Bebop, and Najica being just a few examples).
On a side note: Hearing instrumental versions of songs which normally have lyrics is pretty cool. I've heard instrumentals of Bonkers and Darkwing Duck where they remove the words, and it's fun to sing along to them.