I've always been a fan of Reese's Peanut Butter Cups. Though for some reason, I don't like Reese's Pieces all that much. I can't explain it. In any case, the company recently introduced a "Chocolate Lovers" and a "Peanut Butter Lovers" edition of their classic peanut butter cups.
I didn't compare them directly, by measuing them or anything, but the "Chocolate Lovers" version seems to be quite similar, perhaps even identical, to the regular version. The "Peanut Butter Lovers", however, includes only a chocolate bottom - the top covering of the "cup" is a creamy peanut butter. It's not bad, but I think I like the complete chocolate "wrapper" around the peanut butter.
Incidentally, I think my favorite from them is actually the Fast Break bar - those things are great for a snack, and Wal-Mart has them for $0.44, so they don't cost a lot either. Great for a bite on the run when you just need something to tide you over.