American as in US? Or American as in North American? Cause Canadians make some good shit. Anyway, don't leave out Europe!
Anyway, depends. I think anime is much prettier looking and has running plots which can keep me interested. On the other hand US cartoons are something you can turn on and leave on in the background. And they don't often have a huge plot going for them. Of course, this is the average, not the rule.
For me, I hate Japanese voice acting. People pretend it's amazing but it ain't shit. I'm fine with regular Japanese people talking. But for whatever reason whenever they VA the girls all sound like chipmunks and the guys talk like they're all buff or trying to hard. It's grating. And I'm not a fan of lowest common denominator Japanese comedy which mostly consists of: *insert sex joke* -> *character gets bloody nose, makes loud noise, and falls over* and shit like that. It's boring.
US cartoons have better VA and have slightly less cringy jokes. The humor is rarely clever, but it won't make you want to kill everyone. But these cartoons tend to also be uglier, imo.
So for me... depends on what I want: Do I want to watch something or have something on in the background?