Hnnnn....*Fangirl mode activated. You have been warned.*
Well, It seems to be a Three way tie.
First, I'd love to visit the Homestuck Universe. It would be fabulous! (Mostly me locking certain characters into closets, yelling that I ship them. MY SHIPS SHALL SAIL!)
Then the Hetalia Universe. (Shipping.)
And finally, the Lorax Universe. I don' know which version, however. The Original (I'd try to help the Lorax. Save the trees!), Truffula Flu-verse (If you don't know this, look it up on Tumblr. I'd be killing zombies, being badass and stuff.), or Camp Weehawken (Summer camp with gorgeous men and yaoi ships. YES PLEASE.)
...Fangirling makes the reasons so much more... Fun~