To be honest, I don't really prefer either. I used to watch subs and with anime like Fullmetal Alchemist, Tokyo Ghoul, and The Seven Deadly Sins, I prefer the voices in dub.

Meanwhile, Yuri!!! on Ice, Attack on Titan, and Death Parade I prefer in sub.

Some anime I'm neutral on. Black Butler's dub and sub voices sound almost the same and so it doesn't matter to me. Hetalia's sub is calming and the dub accents are hilarious (actually the whole show is hilarious). The Devil is a Part-Timer's sub is better with some characters and better in dub in others.

Here's s random Black Butler picture to end the chapter.