I liked both shows, but I'd choose The Fairly Oddpaprents over Jimmy Neutron. Both shows are funny, and well made, but I like Oddparents a little more. And when I got older I started to understand and appreciate the adult humor thrown into both shows as well, the kind of humor that goes over most kids' heads.
Boy, I don't get how this a question when everyone know Jimmy Neutron was way better, and I'll explain why. First, c because Carl Weezer was the funniest guy by far out of both shows, with his allergies, funny comments, weak strength, so weak he had so much trouble lifting a pebble, his obsession with Jimmy's mom, and etc. Next, Jimmy's mo is a bad ass as she fought and killed a robot mom of Jimmy's with a broom stick. Next, Sheen was super funny, and it goes on.
In my family they all think Jimmy Neutron is way better and we all didn't really like Timmy Turner. The worst about it was when that sparky dog came on the show, and it me make it go from an alright show to lame.