For me it comes down to what I am used to. I use an Android phone and had the nexus 7 before but had to return it because of a hardware defect. Even though ipad is supposed to be more user friendly, I am just not used to it, so it frustrates me because I don't know all the in and outs. True, android is more hacker friendly/customizable, but I am happy with a pure android experience without oem overlays.
Surface? I have zero faith that MS are serious about RT or windows on ARM, so not willing to go there. and x86 CPUs that can compete with ARM on power efficiency have yet to come out. So maybe next gen.
But what about the kindle fire HD? I heard it's pretty much a tie with the Nexus 7