I have a Weber Sig 8 in mine; my dad has an 8A125 or variation of that...large price difference but his sounds amazing. Fills out the amp much better and more articulate. The Sig is still an upgrade from the original however.
I have one of the old Eminence ceramic speakers in a Champ and a Weber 8A100T in a Vibro-Champ. The Weber has sweeter cleans. I picked the A100T (late 50s R cone) over the A125 because it has slightly more midrange. It is the perfect match for my taste. It is really sweet.