Hey you stole my sig pic! :p
As for the thread topic, yeah I don't really have main either, I use pretty much all weapons and switch between them frequently, but if we're to go by turf inked then the Custom Jet Squelcher is my number one.
Yeah, that's how I do things too, only I want to keep things as even as possible. Now that SplatNet's available in English, if I don't feel like using a new weapon, I just look at what the least-inked weapon I have is and use it for that session until it reaches the middle of the pack or something.
The last game I truly had a main for was
Super Smash Bros. Melee. I got kind of bugged at BlazBlue's online profile cards as it lists your "Main" and "Sub-Main," because I truly have none, that I had forgone the game's built-in character randomizer and kept a tally of each character I used, making sure to use each character exactly once before starting the cycle over again. As a result, my profile card's Main would always change after every match to the character I last played.
After Melee, I decided not to main anything anymore because it got boring. I have a short attention span, so a multiplayer-oriented game can only sustain my interest for a long time if it has many options for play styles and I use them all. I'm also the sort of person who wants to understand a game as much as possible, and there's no way I can do that without trying everything out.