I voted for the fzr.
The way I interpreted the question was how the cars handled, period. Not in relation to each other.
In my opinion the xrr is much easier to drive once you realize the power kicks in pretty hard once the turbo hits. To counter this you can predict the turbo coming on and let off a little to make the power delivery progressive. This makes the car easier to drive at the limits I think, but if your used to n/a power you can tend to get used to keeping the pedal down if there is no power at first.
The fzr is a much more twitchy car. The throttle is instant and it feels like an open wheel car in a way. This car is easier to be fast in, but for the more inexperienced this car is a handful.
I made my decision thinking from the point of view of an intermediate driver. The xrr has turbo lag which wont allow the driver to jam the gas pedal and spin the car out. Instead, if one learns to jam the gas pedal initially and play with it, its actually harder to spin compared to the twitchy fzr. Sure, the fzr is easier to go fast in, but the question is "what is the most-difficult-to-drive GTR car?", not "what is the most difficult-to-drive-FAST GTR car?"