This is kinda dumb Andy. It's like saying what model CHEVY is best, everyone has a choice of the various models, but price will come into play, options, etc.
Same with your processor question here, people with a tighter budget will pick the i5, people with the bigger bank roll will take the i7 and some people will be looking into the future for the Gulftown.
They are all GOOD processors and are ALL capable. There is NO best here, get it.