Personal preference is Heroes atm. Though I'm hungry to look at C#, burning a hole on my storage.
Problem with Mir is, Ruby comes along, there's a mass of dev, everyone feels warm and fuzzy, some dev on their own a tad further, then something else comes along. Heroes is kinda the same, masses of great dev, nice warm feelings, things go stagnant, some dev on their own so there's some forks to versions. Then Apple, bunch of people work together, then split up, people work on their own, whilst the people watching the dev are probably waiting at this point for C# to come along. It's still going to have problems cos the open status was great, lots of great work done by many people, but I can see forks coming. Along the way, the people who dev'd on their own release their old source, which whilst great, is still older versions and is found to contain a number of bugs they didn't look at - whilst many knew about them.
It's all a mess. It's too bad ya'll can't keep everything open and work together.
So much talent working on their own things.
And I don't mean everyone release their server setups, just the basics. Most people edit the editable anyway.