Two great games.
I'd leave this up to your subjective preference for the art and music packages. Just figure out if you don't like either one...
I presume otherwise availability and price will lead you to the answer...
Price is the same on both. These for some strange reason have remained somewhat flat the last 5 years that I've been in the hobby. I'd put them at 2200-2400.
The music/art of Earthshaker is a no-go for me... But that's doesn't say anything about the gameplay... So it's an easy decision. Completely subjective.
In this situation, since sound is very important to me -- I'd play movies of both and NOT watch the game play -- until my ears told me which game sounds like more fun.
-mof