I'm comparing a couple of GNSS front-end modules. Is a lower In-band IIP3 point better or worse than a higher one?
The higher the better (other things equal), because more input power will be needed for the same amount of degradation in linearity. So you will have better dynamic range.

Also, intermodulation noise can reduce your effective \$E_b/N_0\$, thus increasing your bit error rate (BER). The sensitivity of your receiver will decrease.