Fairly Light; i use the same MAC shades as you, & Fair is actually WAAAAAAAAY too pale for me.
I usually end up beginning low end and trying out several types. Do what fits your situation and Im sure your instinct will be right. I like http://BrandsMakeup.com
hi, I use mac NC15 and bareminerals, for the winter I'd use fairly light and in the summer I'd use light as it has a more yellow-y colour to it and gives you a healthy glow :)
I actually prefer the mac foundation because it has a better coveage, but thats just my opinion
Hope I helped