It's too early to tell until the offseason is complete. But, my guess is that New England will again be the team to beat. Brady/Cassel isn't a problem, they can't afford to keep both of them so they'll pick one and he'll be effective. The other will not be on their roster so there will be no controversy. Losing their OC isn't going to be a huge deal either IMHO. What will be a problem for them is age. Their team is very old in a lot of places, and while Brady, Moss, etc. are still spring chickens, there are a lot of players who loose another step each year, particularly on defense. Plus, their secondary isn't what it used to be since they lost Asante Samuel.
But, they've still got the best team in the AFC East, at least until we have to re-evaluate after the draft and free agency.
Let's be honest here, the Dolphins have a lot of holes. Porter is old so we can't expect him to duplicate this season although he'll likely be good again. Roth cannot cover at all, and it's only a matter of time before teams start taking advantage of that mismatch routinely. Ayodele is mediocre at best. Crowder--if he is even re-signed--is mediocre and neither ILB forces fumbles, recovers fumbles, tips passes or intercepts them. Our LB corps is weak. We have 1 good safety (Bell) and 1 good CB (Will Allen) and a lot of mediocrity at CB2, NB, and the other S. We also have no depth of consequence. Ferguson and Holiday are old and should be expected to diminish. So our defense has a lot of holes, and that's our strength.
On offense we lack a big possession WR, a good blocking TE, 1 G, and any depth along the interior OL. We can't fill all these holes in the offseason.
So, I sincerely doubt we'll repeat as AFC Eash Champions.
But it'll be fun trying.