its a lost cause trying to argue. You either see chemistry or you dont.

Imo:

-Delena have 10x the chemistry that Stelena had. And thats pretty obvious seeing that Ian and Nina dated for year and were in love with each other in real life.
-Damon is a more interesting character. At least in the early seasons he was imo. And for me, as a viewer, seeing him constantly being second best was sad to watch and I wanted him to finally get the girl, which he did.
-The DE storyline was so much more interesting to watch play out. They started off hating each other, and then we saw Damon's feelings develop but it took Elena a while to get there. That was fun to watch imo. S/E got togethr in 2 episode LOL. to me, thats boring AF. I prefer couples that have angst and drama.
-As Elena said time again, Damon brought out the fun and passionate side to Elena. He made her feel free and invincible. He loved her in whatever form she was in. And Elena always saw the good in Damon and knew he was worth saving, which no one had ever done for him before. They both brought somethign to the other that they needed. S/E were fine and they were sweet,but they didnt really challenge one another or cause the other to grow in deep ways.

Once SE broke up they barely even shared scenes together or were that close.

B/D barely had scenes/disliked each other for the first 5 seasons of the series and didnt get much in season 8 due to the fact that Bonnie was choosing Enzo over him. So really, they only had 2 good seasons (6 and 7) where they were best friends. I enjoyed those scenes a lot but it was very platonic and it wasn't cared for in the same way as other pairings.