The museum would be nice, so then you'll have the upstairs show case rooms for storage and other junk. Dream suite can be more important later for when you design and decorate your town plus it can give you lots of ideasssss ;D
Museum. It gives you extra room storage, should you want it and you can buy silver tools. The dream suite can be done at any time. Since I'm assuming you won't have unlocked everything else on main street yet, not having the dream suite there a while longer shouldn't hurt much