I've played most of the series, and Monster Rancher 2 is definitely the highlight. It's probably my favorite PS1 game. I don't know much about the DS version, but part of the fun of the early Monstet Ranchers was trying every CD in the house to see what monsters came out, and I doubt the DS game can compare to that.
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Muglekoopo14
Wakka wakka wakka *consumes you*