I alway use subtitles, because I (like most people) read a lot faster than almost anyone can speak.
I wholehaeartedly agree to this article:
http://www.escapistmagazine.com/articles/view/columns/experienced-points/7588-Experienced-Points-Voice-vs-Choice
I very much agree with that article.
I would like to add to that that text to me is more immersive than voice acting.
For the exact same reason the book is always better than the movie.
Because I invent my own voice. Because the actor doesnt say things 'wrongly' (other than fits the character I imagine.)
Im not a fan of full voice acting at all, but I suppose it would be silly to want them to go back to text, even though that would make a far superior game.
I guess well just have to wait until voices can be synthesized sounding naturally until we get decent choices in our RPG's again.
I always use subtitles myself as I am not a native English speaker and its easier with text not to miss things.