Don't forget your feet. The most important thing is that the boots fit your feet. You can't change your feet if the boots don't fit, but you can change the crampons!
After that, consider the use you want to put them to. I only do walking, not climbing, though that can be over pretty steep / rough ground. So I need some give in the boot for all day comfort rather than a B3 totally rigid boot.
I use Raichle All Degree Lite boots (the older B2 model, not the newer B1 version) and can't recommend them high enough. They have always been very comfortable, though I need to be careful in their lacing to avoid heel slop. The boots are lighter than any other crampon compatible boot I have seen too. I use Grivel G10 crampons with mine and the combination seems excellent (though they are a C1 crampon).
YMMV, so try on a lot of different boots to get the best fit.
