I also think those two teams have the best chances to make the finals.
The pistons are the most prepared and consistent team in the east and is really one level above everyone else, add home advantage on top of that, they shouldn't have much problem reaching the finals. Well, maybe some resistence from the heat or the bulls, whichever comes on top.
The Spurs imo are the best team in the league, record wise they are behind the Mavs and the Suns but what's scary about this team is that they never seemed "serious" or played 100% in the regular season, they won a lot of their games without even trying too much. How many times have we seen Tim Duncan playing only 28,30 mins and half of their roster registering double digits in points? Not only that, even those games in which they seemed to struggle and won by a relatively small margin, they actually always had the situation under control, what they often do is they build a 8-10 points lead at the early stage of the game, regardless whether the other team is the Pistons or Bobcats, then start slacking off, dream walking or switching to some "bench training" mode until their opponents are about to close the gap, Realizing they might want to be a bit more serious the spurs would creat another 8 points lead in 3-4 mins, again. They are really that good but boxscores cannot reflect such dominance. Overall I think they are the most "taking the mick while beating you nicely" team in the league, they might not appear so though, thanks to their boring ass playing style. when the playoffs begin, spurs will go 100% with Duncan and Manu playing more mins and all other veterans showing their playoffs and finals experience, that upgrade will make them head and shoulders above everyone else and hence the team to beat.
I really want to say Phoenix vs Detroit, but I know Phoenix can't make it past the Spurs. They could beat the Mavs, but not the Spurs. The Mavs can beat the Spurs, but not the Suns, IMO. Houston probably can't beat any of them right now. No one else matters.