Well it depends.
If you intend to keep a set up with a 2 ohm load, I would go with the MCD1500. It puts out more than the MCD2500 at that ohm load.
However, if you intend on changing your set up to a 1 ohm load sometime in the future, I would go with the MCD2500. It puts out a lot more power when using a 1 ohm load.