I'd rather have subs.
With subs, it's the real script, and all you have to do is read it. Some people complain that the subtitles go to fast, but I've never had that problem. Also, nothing's cut out, and you get to see what was originally put there. Some people complain that the quality isn't good, but it's all a matter of finding the right ones. Also, it can help people to learn the Japanese language. My Japanese mom is too busy to teach me, and I still know quite a bit, most of which I learned from watching subs.
But with dubs, it's a matter of who's dubbing it. I can't stand 4kids dubs. It's not the real thing anymore. Parts are cut out, scripts are changed, the VAs aren't very good (in my opinion) and even the names are changed. In many cases, they also take out the Japanese culture, because for some reason, they want it to seem American. Also, the theme songs are often changed. I love Japanese music, and the songs choosen - or made - are never really appealing to me.
Fandubs are a different story though. Most fandubbers look carefully for people who suit the characters vices, and they use actual epsiodes, without cutting things out. Although, I know of some that have altered the script a bit, but I don't find many.
And that's my opinion :animesmil