I'm a Boston fan and I only pick the Pats,Sox, Celtics, Bruins. Honestly I have no idea why anyone would want to start a franchise with the Heat, it's almost like cheating in a way, especially if you plan on making trades or something. I like using the Celtics because I'm a die hard fan but also because you don't need to make a single change until the offseason, they are pretty much already a dream team.
The ultimate sleeper (and yes Im being biased here a bit) is the 49ers. If you can get a solid QB early in your Franchise you've got a solid team to play with. Just by changing QBs I think my over all team rating jumped around 88 or 89