I'm principally a fan of American football, and for GM duties, I think Front Office Football is the best out there. Not flashy graphics, not a really great "sim the current world" game, but for making decisions under a salary cap and drafting/developing players, it's unmatched IMO.
I have gotten great fun from my times playing the various Football Manager games, too. I don't know very much about soccer, but I still enjoy that game - its depth is miles ahead of anything else out there.