Hi Alan,
aperture always wins at the end of the day, - whether we're talking about bins or scopes. With more aperture, of course you get more of everything, including the city glare, but you either put up with it or move away - or try a couple of filters which can be effective in a limited way (see bintels filters section for guidance).
Your only consideration now it seems, is what size. Really Alan, for the two sizes you mention there, there won't be any noticeable difference in perceived glare from the city.
I have a couple of pairs of 100mm bins and city glare or no city glare, you definitely get to see more of the good stuff too. Get the 12x60s. Hey, you can always get the 20x90s the following week
