I own an FRS and was looking at an S2K at the same time when purchasing. I've driven every generation of S2000 in anger at autox. Also love verts. Or "very" as another thread had!
The FRS (in my region) I could buy brand new for the same price as an S2K that I might be happy (very difficult to find a clean white one without mods/horrors/gremlins/rebuilt...)
The S2K has the much sweeter driveline. My biggest gripe with the FRS is the sound of the motor, sounds grainy. While the FRS/BRZ shifter is very, very good... the S2000 is the best I have used. I have driven many h-patterns, nothing beats the Honda. The FA20 in the toyobaru has a torque dip that is annoying right in the middle of the rpm range (3.5k) whereas the honda has the sweet vtec kick.
They both are very fun to drive, with eager turn in. The S2000 has the better turn in but it is a little less friendly and more difficult to maintain slip angle in. The toyobaru is very approachable in this front. You can easily do an entire autox course sideways (not recommended ;))
The cockpit is superior in the toyobaru for driving duty, the best in this segment actually. The sitting position is excellent and better than the s2k, the wheel is adjustable (not in the s2k). I would describe it as you sit in the toyobaru whereas you sit on the S2K. Also while the S2000 has precise steering it does NOT give a lot of feedback, very numb. The FRS on the other hand has nice weighty steering, an excellent wheel and gives plenty of feedback. Very porshe-esque albeit on a budget.
For track work, although you didn't ask I would take the toyobaru every time. It has better aerodynamics, is more stable and performs much better than anyone would expect. The S2K will need a wing and a rollbar to be approachable at 10/10ths on higher speed tracks.
The brakes are slightly better on the FRS and there is an excellent AP Racing option that saves 10 lb per corner. I also believe the FRS has the potential to take weight out easier while maintaining some civility over the S2K. Pretty easy to get it into the 25XXlb range as most STX guys are I believe.
The aftermarket for this car exploded like nothing else I have seen in the last decade. The car handles boost very well and you have many options for adding power, aero, loosing weight and aesthetics on a relatively new car. Also I believe the motor has more potential to make power N/A than the F22 (not net power but delta/$). I believe the F22 the best bang for buck is test pipe and a tune. On the FA20 headers and a tune eliminate the torque dip and can pick up nearly 50 lb/ft midrange. Imagine this car less 150 lb and with an extra 30-50 hp, which is very achievable. If you have e85 just a tune can let you jump from 170 to 200whp on an otherwise bone stock car.
I love, love roadsters and the look of the S2k but honestly the aesthetics on the toyobaru rub me a little better. That window line and profile is very similar to the new, achingly gorgeous F Type Coupe. But this is opinion. I get plenty of compliments and most people (non car guys) assume the car is either much more expensive and/or packing more heat than it actually is.
To me, this car is a poor man's cayman. Since new/used is a can of worms that I find pointless, I think this is the best NEW DD-capable driver's car you can buy under 50k. The cayman being the best but at a higher price point. The s2k is more like a gt3: more fun to flog around and more special but for year round DD duty too compromised. So I got the better car for the 98% of the time that it will be used as a DD.