My first guild was composed of me and a few friends of steam. *makes goofy heroic pose* We were the Steam Knights. It quickly died as my friend who created it basically quit and I'm not much of a GM so I deserted.
Later joined Volcanic Funfest, that guild was some fun times, it started dying when the GMs left, Golza left it and I followed later afterwards being more or less the last one left in it asides from a very small few.
Knightmare, well...I have my reasons, but I'm still trying to think about it. I loved some of the people there, but something was bugging me there and I felt like I needed to get away from it.
Now I'm with Guild. I have to say, I don't think I'll be leaving, but I might go guildless for a while if I did leave it.
I've never left my first guild because I've been given the responsibility to take care of it even though our Guild Creator cannot play Spiral Knights due to computer issues. I would love to leave our guild to join Knightmare purely for the name but meh, I've been given the task to revive the guild to it's former glory and I intend to do so.