I'll comment since I own both...
The Boss 302 is a fun car (have the VXL brushless model) and it was my first 1/16 scale car. It's a handful with the slick tires on it, but other than shock oil, springs, and a few small things, not much you can do to it.
I have the first gen Sprint 2 Flux w/ AM radio and non-waterpoof electrics and this was my first belt drive car. I've always had shaft drive stuff (RS4, Savage, etc.) so belt drive was new to me. You have to be careful on the surface you run, but I've not had any issues running on the street (yet). I know some people clearance the rear diff carrier to ensure no rocks get stuck in there. I am running it with a 5K Nimh pack and it's a lot of fun too.
I guess if I was looking to buy and those were my two options I'd go for the Sprint 2 Flux. The new one is 2.4 Ghz, waterproof, and even comes with batteries to get you going. The 1/10 scale means you can easily find your favorite body for it, and there's a lot of upgrades for it too (carbon deck, towers, shocks, etc.). Regular 26mm wheels work on it too.
HTH...
Mark