I've only been on Flickr a little less than a year so I have limited experience. It's fine for my purposes which is a place to display my photos so others can see them. I started using Flickr when my printer died and I refuse to buy another. My photos look better on paper but displaying them on Flickr is a decent alternative. I pay for the "Pro" level so I can post unlimited images. I'm not into social media at all so the other photo sites are not interesting to me but I like following other photographers whose work is interesting. Many of them post here on RFF.
I do admit I was hesitant to post on Flickr due to knowing of image theft from the site. That's something that can happen to anyone no matter how careful they are. And, really, there's little to be done other than spending my entire life online to search for stolen photos and then paying an attorney to write threatening letters. Oh, well, that's not for me. As for avoiding posting photos of friends, family, etc., that would restrict my photography significantly. I'm just a snap shooter and I take pictures of everything and everyone and everyone's things. Not to be an A-hole about it but once a photo is taken it becomes mine and I can do with it what I want. I'm pretty sensitive to people and I've deleted lots of photos I felt would be in poor taste or would appear to ridicule the subjects.