He's my experience, being a chocoholic and a cruiser (bad combination!)
Animator's - Double Fudge Chocolate Cake is excellent very chocolatey and moist, definatly one to try, I love it!!!
Parrot Cay - Chocolate-Espresso Walnut Cake had an interesting taste to it. I love the cake (it has big lumps of chopped walnut in it), but I'm not too keen on the sauce, it has a very very strong espresso taste.
Tritons - Don't miss the Grand Marnier Souffle, it has an excellent chocolate-orange taste to it, the sauce is beautiful!
Master Chef - definatly go for the Chocolate Decadence! It is heavenly! The cake itself is made of sort of a thick mousse, it's excellent. (Also I have to recommend the celebration cake, not chocolate but excellent.)
Also don't miss the chocolate covered stawberrys and the little chocolate cake squares they have at midnight snacks!
Also make sure you always check Beach Blanket Buffet or Parrot Cay each lunch time as they have some great chocolate desserts, one it particular they have on some days looks like a small chocolate dome and it comes with vanilla sauce. Can't remember what it's called but it's amazing (but watch out it's very heavy!).
Unfortunatly there is no Lava cake on the Wonder. It is served on the Magic on Captain's Gala night (Thursday).