I usually find it hard to try and order things like this, but after my pretty good 2012, I find myself wanting to go back to certain park, to get back on a certain coaster, as I only got 1 ride on it!
Tonnerre de Zeus!
I'm actually contemplating a return trip to Paris this year just to get back to Asterix...
Also, honourable mentions go to: The Ultimate, Wild Mouse (BPB), Big Thunder Mountain (Paris) and Superman la Atraccion de Acero.
At the moment is Enigma, but only due to me having only ridden around 10 coasters, all of which were kiddies coasters, Hopefully soon I will get to towers and it will change.
I forgot to mention Oblivion and Stealth. They are two coasters that have got better as the years pass. Both are very short, but they both offer an incredible experience.