I've always thought Leppa Berries were pretty bomb. I mean, Ether in Pokemon games is so rare, and you can't buy it in any of the shops, but Leppa Berries are always there for me.
My second favorite are the Jaboca and the Rowap berries, because damaging your opponent's Pokemon is always a fun bonus!
Oh, and my third favorite is probably the Custap berry. That can save a Pokemon, if only by the skin of their teeth!
There are so many good berries out there... Man, some of them look pretty tasty too! *Gobble Gobble! Crunch Crunch! Snarf! Gulp! Gomp Gomp! Nom Nom Nom!*