Played around with all four. I've played operative probably the most. I just started a medic, and I think I should have started as one. I find I get way more XP per match as medic than any other class. Really enjoying medic at the moment.

Recently, I like to play as a medic. There's just something about the field regen unit that gives you complete control over where your teammates stay.

Operative: I just enjoy the spy theme. =P
Second is medic, namely because I do like to help out my comrades.

I play as the soilder a lot due to molotovs, flashbangs and napalm grenades. I play operative 2nd most.

My Light Soldier is my most favoured character so far, the ease of use and resupplying ammo to Heavies who weren't smart enough to be Soldiers.

I really liked my light weight medic class. The combo of speed, health buffs and self-revival is a hard thing to move away from. Plus the character I built has a few handy primary abilites for Engineer and Operative for when I need to switch.

I've enjoyed all though, to be honest. It really does change the game style up depending on what character class I'm working on.

Turrents and Mines.

Always been an Engineer fan when playing a team based game no matter how good/bad the class is.

There is an http://www.gamesas.com/index.php?/topic/1182911-unofficial-brink-poll/ that is the same as this, no need for two thanks.