Most likely at the in-laws this year. Next year it will be at my mom's house.
In-laws are close enough that we could drive on Xmas morning after the kids get up and open presents, but then we'd have 1.5 hours of them complaining/whining that they wanted to bring all their new toys, and spend the day complaining about going home. Easier just to got to the grandparents, have them open some small gifts there, and then go home on Xmas afternoon and they get to open presents again...
As for my mom's, it's about 1600 miles so when we go we're stuck. But they do get another Xmas when they get home, thanks in part to our dog sitter who we sometimes get to play Santa for us by putting out the gifts.