Just because Jasper's also kind of a bad guy (or used to be) like Damon, and Alice is the good girl like Elena. Alice saved Jasper from himself just like Elena saved Damon. Alice is the most important thing to Jasper and he'd do anything to protect her, just like Damon would do anything to protect Elena.
Jasper & Alice love each other more than anything and, well Elena is not there yet, but Damon does love her more than anything and Elena will feel the same way about him sooner or later.
Plus, I believe that Jasper/Alice are the only great couple in the books, the others all suck. I wouldn't compare DE to couples I don't like.

KathyHalliwell: yes i totally agree. i just noticed now that damon and jasper have one more compare: they both were in the civil war and loving fist a girl wich manipulate them: jasper with mariea, damon with katherine.

^Oh yeah, I've noticed that too before, I just didn't think about it when writing my comment. But it's great that you pointed it out :)

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I think they're unique in their own way, but if I had to pick then I would definitely say Alice & Jasper <3