Chicago gave the Heat so much trouble, that they went zone & still couldn't guard much. Pure speed won't always work if Miami can work them inside strong enough. It all depends on who gets into foul trouble, & enough people getting back on defense.
Dallas is composed of mid & long range shooters. Posey can play some good D, but J Williams isn't too interested. Dirk won't have smaller players guarding him, so he might have to move away from that free throw line.
I see Phoenix playing on or off every night, but not being able to run the series to six or seven. Dallas will play a more even matchup, but won't be able to hold on at the end of tight games.