Not a big fan of those skins, since they look too much cartoonish to me. Probably I will go with Warlock since I still dont have 1000 wins portrait for him and I dont like normal Guldan portrait. I like all tier 1 sets from WoW and I am glad that they made them in Hearthstone but would like if they put a bit more effort in them, but since they are "free" they didnt have to invest a lot of time.
Beside Warlock, maybe would consider Demon Hunter but honestly hopping I can get 1000 win portrait because that one looks pretty sick.
Guldan. I already have a 500 win Warlock portrait but I've given up on 1000 because it's too stressful and getting any wins is just a slugfest right now. At least with this one I know I'll eventually get there.