I don't know photobucket, but I have experience with 500px, and don't recommend it. 500px is rapidly turning into yet-another “social” beehive that does nothing to differ itself from others. It no longer appears to pursue high-quality images; instead, it seems to be doing everything to invite more and more photographers, whose work is, shall we say, just not that good. The average lifespan of any new upload is under 1 hour – after that, your work drowns in myriads of new uploads. The “Pulse”, the 500px rating system, is heavily rigged and in no way reflects the real popularity of your photos, and even less, their merits. Rather, it reflects a member’s networking skills and/or use of bots. You may still see many good photos on 500px, but don’t expect too much in terms of exposure/promotion. If 500px goes on doing what it does, it will very soon become the next instagram.