Okay, I know I'm way late on this, but I'm going to say it. Crossovers are the worst.
Ben 10/Generator Rex/ Secret Saturday
The worst by far >>> The Simpsons/Family Guy & KND/Billy and Mandy
Seriously you got two shows and two heroes, you can't make them work out no matter how hard you try.
Can't either show not try to connect to the same universe? Can't one show be from another world? I can't do crossovers in television. In fanfiction that's the only place where anyone and I mean anyone can make a better crossover than the people who produce these shows.