I'll probably go for England; but I might actually pick Scotland to see if there are any differences between the associates and test nations.
One thing that I don't expect to see in the game, but would be really cool, would be to allow players who play for associates nations who are too good to accept offers to play for a test nation they are near too (a bit like Boyd Rankin and English ODI/T20 cricket; or Ed Joyce in the past); or vice versa if for whatever reason, you couldn't break into your own international side (the only one I can think of offhand is Geriant Jones, who played some cricket for Papua New Guinea last year and i think still does if it doesn't class with the English county system). Perhaps something for the future!