I voted for Curaga, but what I really mean is the whole restorative section of magic. Regen is very useful, especially the FFVII version where recovery is constant. Full Cure would be better if it targeted the whole party, but that might make it too cheap. I've just thought - wouldn't all magic be pretty useless without Osmose? Tents are expensive, Ethers are rare and visiting Inns in the middle of a dungeon is nigh on impossible.