I would go for the latest Fly Viper if I were you.
It has excellent speed right out of the box, and in addition has stunning looks.
The Ninco Honda NSX is a very nice fast car. The latest Fly Vipers are very fast too, but feel a bit too stuck down IMHO,relying too much on magnetic downforce. The Ninco Honda has a very good balance between magnetic downforce and tyre grip.
I've not raced the Ninco NSX, but have read several comments that it is much slower than the Cartrix NSX. However, I have both the new style and old style Fly Vipers, and would agree that they are hard to beat. The original was more driveable, and I personally preferred it's handling, but the new version has so much raw power from the Fly Racing motor that what you lose in corners you more than make up in the straight.
My other favourites would be the Fly Venturi, and Lister Storm or the Scalextric TVR's, and possibly their new Viper Competition Coupe, although I've still to race mine seriously.
I guess a lot depends on the track surface and layout, as to what will work best.