I'd join the JLA for two reasons:

1: they've got a frickin' space station!

2: DCU heroes get love from the public. I mean, c'mon! The Flash has a museum!

AS for joining the X-Men...um, how often has that mansion been destroyed? And so much infighting...I swear the X-Men have more problems in their own camp than any other team I've ever seen. They fight each other more than they fight bad guys. Not to mention that no one in the world likes them. I'd join the Power Pack before I join the X-Men...