Best online community for Lego Builders?
I would still recommend Flickr as the number one place. It allows everything you mentioned, and the most important thing is that's where most LEGO fans and all the best LEGO builders hang out. It is by far the best community. Just join some of the main LEGO related groups and you will quickly find people to follow. 

Also, follow the Brothers Brick blog. Pretty much everything they feature is from Flickr, and they focus on the best MOCs. This is another way to find great builders to follow.

There is also MOCPages, and there are some great gems there, but the site is mainly full of little kids. AFOLs and serious builders hang out on Flickr. It may not be all LEGO related, however once you become part of the LEGO related groups, you will have some much to do, so much to see, and so many people to interact with, you won't even notice that Flickr is not all about LEGO...(c: