Sounds like my use case for Flickr differs a lot from the ones mentioned here. I don't store everything there (Over a terabyte of raw photos etc is not worth publishing;-), only photos I want to publish as an enthusiast photographer and see other photographers photos + talk about them. For that Flickr still trumps over 500px, Facebook* and any other service I've seen. Would've probably quit photography as a hobby multiple times without Flickr.
* Facebook is where other people are and there are some good groups but for really following other photographers it sucks + FB molesting JPEGs is just horrible.
FB molesting JPEGs -> upload them as PNGs, reasonably sized and pray. with a bit of luck, none will be reprocessed into crappy JPEG with highest compression available effectively ruining them (yeah, shame for FB, generally it's a piece of sh_t when it comes to technical quality of the site, albeit much better compared to what bugfest it was few years ago)
Instagram. You can use hashtags to organize your photos similar to Lightroom and tag your friends to keep track of who's in them. I also found out if you use the hidden "Full Ten" filter it retains the original quality.
Instagram is a horrible image portfolio system. It does not offer full res downloads, has zero exif data, extremely limited desktop app. Instagram is a social media app first, and a photo app second.
500px is apparently where all the cool kids go. I use Google Photos.
(500px has a really weird community. The hive mind likes photos edited to have a certain look, and there are lots of random people that show up to like your photos in the hope that you will like theirs, and they'll get popular enough to be featured on the front page. As a result, I don't use it. My friends on G+ are enough sharing for me :)
