04 was better. More talent 1-53 than 03.
Also, while 14-2 is impressive and back-to-back is even more so, the 04 record was the stronger of the two based on who they had played. In 03, they lost two road games early but to vastly inferior teams. They were rocky for the first month of the season. Win one, lose one.
The 04 team was flat out dominant from the start. If the Pats don't lose Ty Law, Corey Dillon, etc for the Pittsburgh game, that team is 15-1, hosting the AFC Championship game and possibly 16-0. The only game that they "lost at full strength" (a relative term given the secondary) was in Miami when they sort of let up and Miami kicked the door down, something that they have not really allowed themselves to do since.
After week one (a three point win) the next closest victory was 13-6 over the Jets in week 6. The had two more wins, at KC and vs Cinci, that were within a single posession; and really in neither of those games did it feel like the Pats were not in control. 14-2, with 10 wins coming by more than ten points is a dominant team with six games vs playoff teams. 5-1 vs playoff teams in the regular season, if you include the playoffs they were 8-1. 9-1 vs teams that finished .500 or better. No real comparison between the two years IMHO.
That being said, 03 was the season I will relish more. Not many picked them before the season, it had more "memorable moments" with the snow games, goal line stands, OT victories, games in horrible rain, etc. Every game had a storyline. In 04, after getting Dillon, the Pats were the favorite and the pressure is on. As a lot of players will tell you, it is hard to have fun when you are expected to win every game but this team found a way to almost do just that!