There shouldn't be any competition. Both grandparents are there to love the GD's in different ways. Be glad they are kind people who give the GD's a happy time. Share. It won't always be equal...but I cannot see that sarcastic comments will help the situation. Gifts are gifts, not ways of buying entitlement.
When my first grandchild [now there's 2] came along the other Nanny would look after him for a day at a time in her own place. She fed him, soothed him, took him out in the buggy, changed nappies etc. I saw him in the evenings and he was in his own environment with his own toys and we just played and had fun. I would take him out to the cinema or bike riding when he was older and played cricket and football with him. The other Nanny didn't want to do that. It worked.
My other son now has 2 children. They see their Nanny and Grampy a lot. They have sleepovers there and they all go on holiday together [often abroad] and have a marvellous time. I can't do that, but am delighted that they have the experiences they do. Also their 3 cousins live next to the grandparents too so another good reason for them to be there a lot. I contribute in other ways, pick them up from school, take them swimming, and do activities at home with them.....reading, writing, painting, drawing etc. They think I am funny!
My DGD came to my house the other week, quickly gave me a crepe paper/pipe cleaner flower and said she'd made it for Nanny '....but you can have it Granma'. I just laughed. Did I think I was second best? No, we are just different. No offence intended or taken. Kids eh?