Funny of you to say that, I actually think playing the Dolphins is one of the easier teams in Madden, at least compared the the others you posted. Their QB is bad, sure, but that's something you as a user can compesate. Marshall is a very good receiver in the game, and Bush may not be the best back, but he's got the speed to create some big plays for you, which is really all your need. Their line needs some work but since Oline is the only position in the game that's easy to scout that shouldn't be a problem.
Their D isn't looking half as bad as you think it is, they got one of the best CBs in the game who can actually get just as good or even superiour to Revis in a couple years.
The Dolphins, as they are in Madden, are only one decent draft away from being a contender in their division.
The teams I've had the most challenge with are the Seahawks and Cardinals. They both have huge holes all over the roster but of course they don't play in a good division, if you want that, I'd say have a look at the Redskins, they lack a QB just as the Dolphins do, but they have a lot more holes on the rest of the roster and they play in a very tough division in Madden, as long as Vick stays healthy and fast he's a nightmare to play against, and both the Cowboys and Giants are strong teams in the game.
Vikings are an option, too, of course, but they really have enough on offense to keep you in most games, especially since they already got their franchise QB and in Madden, it's not a question of if a first rounder pans out, just when.
Panthers may struggle when controlled by the CPU, but Cam Newton is a ridiculously effective weapon when user controlled, just as the Vikings, their offense will be good enough to make you competitive in pretty much any game you play if you know how to use Newton.