Good question, from my situation my DM gets on very well with DH and vice versa, she thinks he is great and tells him so.
My MIL is pleasant to me on the face of things but arranges family meals including all family except me, DH & DD, always turns down my invitations to spend time with DD on bank holidays etc (when I know she is off so may ask her if she would like to come for lunch with us/go to park/come to DDs playgroup) by saying she is busy or had other plans, yet she complains we don't invite her round?! Or says she hasn't seen DD for ages!?
To be fair, not being invited to things isn't entirely down to her, the other guests don't invite us either (SIL, GPIL) so can't be laid entirely at her door. Latest example is they all went out for SIL bday, we didn't get invited but MIL brought us some cake from the event, thanks! To me it's like - we didn't want you there but look, aren't I being nice to bring you some leftovers from our nice day out.
I find it quite hurtful but have resolved not to make the effort anymore, DH says I shouldn't bother with them, I don't know what the problem is... I only make extra effort as DH works weekends, so I felt that it would be nice to make the effort with them so they can see DD at the weekends when they are off but it always gets turned down so I am giving up on bothering.
Sorry, that kind of turned into a moan, basically, they are nice on face of it but not very nice under the surface, my DM goes out of her way with my DH, but she genuinely likes him.