For what it's worth, I like my paid 500px.com pro account. Worth it for me, even though it is, I feel, overpriced at $20 a month. Still, I have a very nice online portfolio (see my .sig) and it is worth it in the end. Certainly I prefer it over flickr or any of the others I've tried.
I don't need the Pro on 500px, so the Awesome is enough. I'm in the process of converting all my work I want from Flickr over to 500px now. It's a slow process, but good as I can weed through and separate the wheat from the chafe.