Preferred Servers...?

[shooteneq1]

Im wondering how does a server become a preferred server? im just curious because i was playing on one and for 3 days straight it was laggy, server crashes and rollbacks. i only played on it because i figured if it was preferred than it was stable and wouldnt have issues like this. i get they are free servers but imo if you are going to ask people to spend their time on your server then you need to maintain it. i feel like i just wasted 3 days. maybe preferred server means something else i dunno, im just curious though what the criteria is for it.