I think I am most excited for Gamzee-Karkat-Dave interactions.

Gamzee and Karkat because their relationship as Moirails is hilarious and adorable to me. 

Dave and Gamzee because I want Dave to meet up with his favorite troll again, genuinly like him, and see all the batshit crazy that Dave accidentally pushed him to. Plus all of the rap battles.

Karkat and Dave because these two have to be the top snarkers on the ship and would love to see them more/less snarking at each other the entire time.

And combine three, and you get Karkat annoyed as hell over Gamzee and Dave’s rap battles, and Karkat angry as hell when he finds out what Dave did to push Gamzee. It will just be glorious to watch.