Some dubs are surprisingly well done while others appear to have come out of someone's worst nightmare. Subs really depends on how good the subtitles are. One thing I did notice through the years is dubs for foreign films are done quite poorly.
This so much.
Subs have and always will be more convenient, but that race to be first sub group out has had some serious quality drops. There are just grammar errors and sentence structure problems all over the place now, simply from careless mistakes. When reading casually our brains just skim over stuff like that, but when there is an error, sometimes it catches your attention way to much haha.
On the other hand dubs have come a long way since the early 2000s, and for those like me who remember anime even before its big global boom, WAY better lol. However it still is based on which actors are used, and most importantly the translation and editing of the script. Making it flow right, and most importantly making it have "context" to the area its being translated for is super hard, but when its done right, it's amazing.
Great examples of that are, FLCL, Disgaea video game series, and more recently Gundam Unicorn. FLCL had all its Japanese references taken out that 99% of people would not understand, but were replaced with what would be their English equivilant. Same with Disgaea. The joke or meaning remained and the effect was not lost, but the context was changed for the better. Gundam Unicorn benifits from being dubbed at the same exact time as the Japanese version, and a high enough budget that the translation simply must be done well lol. Having the actors for both sides next to each other giving tips on how to convey the character is having a major effect on the quality too!
Personally prefer dubs for conveying ages. In Japanese dub lets face it, you are either 6 years old or 45 lol. Using Gundam Unicorn again, Audrey sounds 16~mid 20s in English, in Japanese she sounds straight up 40 haha. Also English dubs tend to do antagonists extremely well too, like Char and Full Frontal have great voices, tons of "gravitas" when they talk, which is EXACTLY how the characters should be.
While I watch Unicorn in the dub (since it comes out the same day as the Japanese version) Its just impossible for me to accept the ENG dub of Gundam 00. Which mostly comes down to "what you hear first." I don't think enough people consider that when they prefer one version to another. Then again sometimes some voices are annoying in both languages (cough Shinji in Eva cough)
Either way, its all still a crap shoot. For every great Japanese dub, there is an awful one that Japanese people hate too haha. Same for English. Pretty much both sides agree that sometimes, the other regions dubs are better.