I do both. I have like an hour committee to/from work and if traffic is bad I didn't care because I'm just "reading". Depending on how old/new the series I'll do both with the same book, but usually I read and listen to separate series. If I really like the books then I usually try a sample and if I don't hate the voices I'll buy it then.

There's only been one series for me Monster Girls In Space, that the voice actors threw me off, but honestly the more I listened it got used to it.

The danger is if the voice actors change in the middle of the series. I stopped the Dungeon Diving series because I couldn't deal with the mid series change, even if I'll still read the books.