I've used both, and they are great.
Try to work with the fact they aren't that great in English.
Btw, what exactly are you interested in buying from them?
Well, Gold4rs got me 10 mil in 4 or 5 days, and Usfine powerleveled my MapleStory account from 44-50 in a day, so I think they're both good. Personally, I would pick Usfine.