The only reason I'm considering playing a Heavy over a Medium is because I'm concerned the pump action shotgun (which isn't a one shot kill) won't be able to outdamage an automatic weapon at point blank range, yes I know that's a lame reason.
Maybe I'll make a Medium AR/SR Soldier though, Lights are probably going to be too flimsy for me to be drawn to them even with their high speed and more accessable SMART.
Light Rifle/Shotgun FTW
In the reactor video, it looks like the guy was taking out medium players in 2-3 shots at a decent range, and then finish downed people off in another shot.
http://www.youtube.com/watch?v=Mho-QeFh0Kk&feature=player_detailpage#t=6m50s
Even if the the shotgun takes just as long to kill someone at close range as the AR, being able to duck for cover inbetween shots is useful in CQC.
Edit: I just noticed that at the end of the clip, when they successfully manage to destroy the reactor, the computer says "Meltdown imminent, have a nice day" :foodndrink: