I slackline every so often. Helped a ton with my balance, and is cheap. I have been longboarding for a bit, but only this summer got into skateboarding. Longboarding is easier to get started imho.
My main longboard is the NS decent V2, it is kinda nice because it is kind of a mix between a skateboard and a longboard. I also have an arbor assault, which is really nice too.
Skateboarding is a lot more fun if you don't have many decent hills. However, you can still have a lot of fun longboarding on small inclines. Some of the freeride longboards feel a lot like snowboarding which I really enjoy.