The H9 comes with nine algorithms: Chorus, TremoloPan, TapeEcho, Vintage Delay, Crystals, H910/H949, Hall, Shimmer, and UltraTap.  The H9 Core comes with only a single algorithm, H910/H949, and costs $100 less.  Otherwise, they are the same; there are no differences in the hardware between the two.

If you know Eventide's algorithms very well and you're not interested in the algorithms that come bundled with a standard H9, then H9 Core will be more interesting for you.  Or if you already have a standard H9 and want to add a second H9, then H9 Core will be more interesting for you.