***Delena fans this is just my opinion, so please dont post any mean or hurtful comments***
***These reasons are based on Tv show AND book, so some things aren't necesarily true in both***
1) Stefan and Elena genuinely love eachother. They both knew from the moment they saw eachother that they wanted to be together.
2) Them being together wont hurt anyone. If Damon and Elena are together Bonnie would be hurt, because in the books she is crazy for him.
3) Stefan dosen't seem right with anyone else. While you can picture Damon with Bonnie or maybe Rose (If she wasn't dead,) but I can't picture Stefan with anybody else.
4) Damon and Elena would argue over Damons lifestyle. Elena wouldn't be happy with Damon drinking human blood, and if Damon quits for her, he will be completely different.
So they are my reasons for shipping Stelena.