I would have to say that an mg isnt always about getting kills. The main function of the mg isn't to kill, its to give suppersive fire and a base of fire to flank from. If I had to choose between mg or rifle, I wouldn't know off hand. Many factors like what map, what side, whose on, how is the team doing and all that are major factors for me. If we need flags, I wont be mg and Ill start capping. If we need to hold tight, Ill gladly take an mg and guard. ( Its not camping if you have an objective ;p)
The mg is satsifying (spelling is bad, I know ;p ) to just shoot and shoot and shoot and did I mention shoot? I like using it for teamwork and cover fire and all that. I could care less about my score and kills if it means we win the game then.
Now using rifles are fun because the kill feels more personal. Its not shooting 100000000 shots and hoping a few hit, its taking aim and firing one, two, maybe three shots to kill someone. It gives more satsifaction because you had to aim and move so that you didnt get shot, not camping on a ledge with a bipod.
Sorry if this is hard to understand or doesnt make sense, Im hungover like no other.