Most English dubs before the year 2000 are pretty bad. Starting with the 2000s you have the English dubbing company FUNimation who start doing a lot of dubs and they usually tend to be not totally awful. By 2010 most English dubs are decent.
If I'm watching a show as it's coming out, I have pretty much no choice but to watch it subbed because that's what comes out first.
If I have the option between an English dub or subbed, it depends on when the show came out. Older shows I almost always watch subbed.
Anyway, here are some recommendations for anime with amazing English dubs:
- Fullmetal Alchemist: Brotherhood