I wanted to know if there were any differences between choosing sides, thanks

A couple quests are entirely different, some are intertwined, some..the later ones supposedly are the same just a different story leading into them such as the forgotten vale area.

Dawnguard gives you quests to get and make different types of crossbows while the Vampires give you quests to get artifacts to increase your vampiric powers.

There is but not much. From what I've heard you get more benefits for joining the dawnguard.

Ive already beatwn the dawnguard side, i just wanted to know if the end descion is the same when u get to the final quest

If you're a Vampire you can use auriel's bow to block out the sun temporarily for a day while from what I understand if you're in the dawnguard it just makes it rain fire..if you block the sun out all things Vampiric come out and start attacking the roads.

If you mean at the end if you kill Harkon either way?

Yes...I think.

Do they attack you as well when they come out?

It still blocks the sun on the dawnguard side, so at the end harkon dies regardless of which side you u choose