I don't know if favourite, but I spend a lot of time on reddit. I've customized it to only show things I'm interested in, like random beautiful photos from around the world, random advice, recipes, hiking & travel stories, how to improve your life, info on the sports and sports clubs I'm interested in, news from various places, pictures of stadiums, altered maps, random explanations of how things work, new discoveries, "ask a scientist", "ask a chef", jokes, lifestyle advice, science fiction, screenshots of games I'm interested in.. and so on. Many many things that I want to hear more about on an ongoing basis!
I like it because .. well, because it's just stuff I like. It keeps me up to date with what's going on with stuff I like and I get to make sarcastic comments about them. Win/win. It also feels like a bit of an abstract community, which is neat. In many ways it can be silly and annoying and even stupid, but I just find it fascinating that humans can get together in large numbers like this, interact in this specific way, and then go out and do things like help random strangers halfway around the world or organize guiness book of world record events on a global scale or whatever. It's very organic, but like I said before the most important part is that it's useful. I'm a very pragmatic person, so a website that shows me a constant stream of information related to things that I am interested in is just kind of awesome. The fact that i can stumble into what feels like rooms of experts and wannabe experts and ask random stupid questions and get decent or even quality advice and feedback? You can do that on a forum, but forums tend to be more intimate places - with smaller numbers of users. On reddit if you ask a question, you can read all the answers, like on a forum.. one by one, chronologically.. OR you can read the most popular responses first, as determined by the community. Pragmatism dictates that the latter saves time and is more efficient and so I have no choice but to spend hours on reddit each day (asking stupid questions and making stupid comments)
There's even porn there, so you're kind of covered for everything.