I like Jasper because he is understated. Emmett comes across as a bit of a lovable ‘goof ball’, if you will, whereas Jasper has been there, he has suffered and still carries some of that torment with him.
Alice and Jasper’s relationship also has similarities to Edward and Bella’s, I really believe they would die for each other, or want to die if they were apart from each other. I wouldn’t say that about Rosalie/Emmet or even Carlisle/Esme. There is an Eclipse quote, when we find out about Jasper and Alice’s back story;
‘Jasper smiled down at her. "You held out your hand, and I took it without stopping to make sense of what I was doing. For the first time in almost a century, I felt hope."’
Its similar to the Edward to Bella quote;
‘You don’t know how long I waited for you’
In addition, in Midnight Sun, Edward talks about Alice and Jasper, and compares them to Rosalie and Emmett;
‘Though Rosalie and Emmett were more flagrant about their relationship, it was Alice and Jasper who knew each other's every mood as well as their own. As if they could read minds, too - only just each other's.’
I love Jasper for the same reason that I love Edward; their whole existence is about their love for their respective woman.
Am I just a hopeless romantic?!