If you're looking at a cruiser, then the Excelsior is where it's at on DPS. She moves faster, is more flexible (even though the Odyssey has universal Boff slots), has transwarp capability to every sector of the game map, has a strong defensive capability, and is just a terrific ship.
I have the C-store Odyssey (Tactical) and I am severely disappointed in it's abilities as compared to the Excelsior. It seems like it has more advantages, but that's before you account for it's size and capabilities. Even with the +1 stats, it handles about the same as the free Odyssey, and what's worse is that even with the Mk XII green RCS console, the ship can barely get out of it's own way.
While fighting other ships in PvE, the Odyssey doesn't perform very well. It's designed as a tank, but I have much more success tanking with my Excelsior, where I can maneuver enough to regen my shield facings, and use all of my defensive Boffs.
So the Excelsior gives me:
1) Great DPS
2) Great Defense
3) Best maneuverability for a Tier 5 cruiser.
Now, this is just anecdotal, and every experience will differ, but in PvP, I've destroyed a lot of Odysseys with my Excelsior. Others have ended in a stalemate, and one ended when the guy got down to a handful of hull points and escaped. I have never been straight out killed by an Odyssey alone.