Leigh,
So sorry about your Dad. A big hug to you! It's a beautiful quilt and will be a loving touch for your Mom's house. I think machine quilting a criss cross grid pattern would be nice and with a walking foot it goes pretty quick. Of course, I am not a stickler for perfection. I also think it would be nice tied. Either way you decide to go, it is a lovely quilt!
Patti