As part of my fixation(obsession?) with propliners and early airlines, I am currently tracking two kits of the Ford Trimotor on ebay. One is Airfix, the other is Revell. They're both 1/72 and are currently being bid for about $10.00 USD.

Assuming the price stays about even, which is the better kit?

Both are good kits, however the Revell is a repop of a very old Monogram kit. It is not a true 1/72 scale. It's 1/77 scale. It comes with some cool options like skis and a dog slied for an Aritic verison. Detail is good and it can be built up into a nice looking model.
The Airfix kit is better as far as interior and outside detail. Mine looks great next to my Heller JU52