You are not telling us very much. Are they both Coupes? (Roadsters came out in 05, so I'm assuming they are both Coupes.)

Personally, the red (I think they call it Cedar) interior is my least favorite (only cause it's ugly). On the other hand, the 07s/08s have a modified underdash/glove box. Not a big deal, but they are a bit different (this was done due to federal regulations.) The 04s are the only ones with the automatic day/night rear view mirror - other than that, there are no differences.

The 04s with manuals had a 1st gear issue that was covered by warranty, tho many never got them fixed and the TSB has expired.

If one is an auto and one is a manual, buy the manual so you never deal with the auto trans fluid leak or the conductor plate failing.