Pros for NY outweigh the Pros for London by 11:2..... Oh, what a shocker
I've been waiting to post my response here, my 3 dual nationality children are pre-5 years old, I'm not yet dealing with the issues that Yvonne was initially asking about. And Kirk's response was brilliant.
I do however want to lend my two cents to the discussion as it's progressing. Hovis' suggestion is great, and I'm very analyzing about decisions as well. It took me a full year to decide to move here.
I do think that you will need to live where you and your partner can be happy together. There has to be comprimise, someone will inevitably make more sacrifice than the other. So I did make the sacrifice, gave up all and moved. I also told myself that I could not hold my partner responsible for my decision, it was my decision, and I could not be bitter about it or hold it over his head in the future. I'm not keeping score. I sometimes have to remind myself of those things.
Custody issues could be a concern someday, and yes, wherever the children have lived is their residence, and it is a big factor in custody, just as biggest_apple said.
If Glen agrees to raise the children in America as you want to, then that's great. It would make more sense to me to be established where you want to be permanently. I would leave the issue of children out of your decision of where you want to live for the time being. Forget kids for a bit, give life here a real and fair chance, and you might find more things to add to your pro's for living in the UK. If after that you're still set on raising your children in the States, then I would move before having them. And if that's what Glen still agrees to, then you've nipped those transatlantic custody issues in the bud.
Has it ever crossed your mind that maybe you're destined to live here, that things work for the best and there is some reason that you are here? Sounds kooky maybe, but sometimes I believe in silly things such as this, and sometimes I don't. There are also a lot of people who will never get the chance that you have, to explore a "foreign country", don't forget to enjoy that while you are here.
Just my two cents anyway.