My parents live on the other side of the world and it often makes things very challenging for me. My MIL lives 1.5 hours away and babysits when I need her to. She is so great with our little boy and also has a great set-up at her home for all off her grandkids (toys, portacot etc.).

I really do trust her implicitly with our boy and, because he is her 8th grandchild she is very calm and experienced with the littlies. My parents are a bit more cautious - they want instructions from me for everything. They just aren't as confident as she is and I think they fuss a bit more about doing the right thing by both our son and me. So even although I would leave him with them in a heartbeat, the lead-up is often more stressful! The fact that they live so far away doesn't give them much practice either! So no, I don't necessarily favour my parents over my in-laws at all

Having said all of that, my only advice is that circumstances change and you need to realise that in the event of your mum moving away and/or starting work (or whatever), you may well need help and your MIL may be the only one who can help you. To not foster your and your son's relationship (and this does mean giving them some one-on-one time) with her by giving her some room to move and giving her the benefit of the doubt could really impact on your family going forward.

Sorry to sound so prescriptive, but I know how hard it can be to not have help that you always bargained on growing up (i.e. always having your folks around) just because circumstances change. Just want you to know. I hope things all work out well for you