Both are fantastic subs. I've got more experience w/ the Eclipse. This one just comes down to personal preference. I think the Eclipse has better SQ, others say the X.X.X. does. The Eclipse is a monster that can take the abuse. It's under-rated and built like a tank. Both are great subs that not everyone is going to have. X.X.X. is relatively inexpensive to recone.
If at all possible try to listen to both, either would be a great choice of sub.