It was quite fun choosing. Newly-weds often discover that their families have different traditions, and have to find ways to merge them. Forty years on, there was more to discover. I'd had Grandma and Grandad on one side, and Grandma and Grandpa on the other. So I'd not really thought about alternatives, and was quite surprised when my wife wanted to be Nanny. I stuck with Grandad (how many d's are there in that word, I still can't figure it out for sure, but fortunately we say it rather than spell it?)
Our friends/in-laws/etc. chose to be Granny and Grandpa, so there's no confusion at all, and everyone is happy, except for my being even more confused that there is no Grandma in sight anywhere, when I'd had two.