Just wanting some opinions on which classes you think are the best for healing in PvP.

I plan on mainly doing pvp at 50 and was wanting some input on which class you guys think would be best for dps. I'm also interested in what each class' role mainly is.

I plan on mainly pvping at 50 and am curious which the better class would be for dps. I am also unsure as to what roll each of them play in pvp.

I am wondering what would be the best thing for me to upgrade on my computer so that it would run more smooth with my graphics on high especially in major cities. I am not sure how to post my specs, could someone help?