there's no question in my mind of which car would be more reliable, just looking at the track record of both cars-the S2k by a long way. I have owned Hondas for years and only Toyota can compete with them in terms of hundreds of thousands of trouble-free miles.
that being said.......You buy a Box because you are passionate about performance and breed heritage in my opinion. It's rarely a rational decision when you buy a roadster. Plus, a true roadster(again in my opinion) can't have a front engine, rear drive set up.....that's a convertible
My biggest issue with the S2k is the i-VTEC. I have driven two of them on the track, as well as our Box S. Mid-Ohio to be exact.
You just have to stay too high in the revs all the time to get any real enjoyment out of the car-you are shifting constantly. Even sprinting through traffic, the S2k needs to be in 3rd and sometimes 2nd gear a lot. it just has no torque whatsoever to speak of. that's the downside of the otherwise fantastic i-VTEC technology.
The Box S reminds me of my Z06 from a torque standpoint. it just has so much grunt on the low end. It's hard to imagine they can get that much pull out of 3.2 liters. No, it does not redline in the 9's like the S2k, but you don't need high revs in this car to get it to the limit in a hurry.
And the mid-engine: don't get me started. if you ever get a chance to get these two cars in their born-for environments, the track, it would become very clear which of the two embodies the sports car spirit. throttle steering the Box S is something that has to be experienced-you can push the rear to your heart's content(with PSM disengaged of course!), knowing you will get plenty of notice when it's had enough. The S2K just has no middle ground. pushing it through off-camber turns at Mid-Ohio is a little harrowing(at least in my amateur hands). The rear end just comes around with very little provocation.
A long post, but I just wanted to let you in on my experience with both cars.
good luck!