Edinburgh, London or California (lol having a whole state instead of somewhere in particular).

I would definitely lean to somewhere that is easy for international flyers to get to, so London would be better than the 'Burgh in this case (despite being a more expensive place to be in, in general) for the UK.

The only other question would be if we have someone in either location who would be willing to do some legwork on finding places for us to stay. Not that I am saying that people outside of these locations can't look up potential places, but it is better if we have someone who can say "Whoa, no, don't go there!" or whatever. xD