Test drive both cars. I can garuntee that unless you are passionate about rotary "sports cars", the RX-8 is not for you. I say this because they are actually very terrible cars. It's not fast, it does not get good MPG even though it has no power, it costs more to maintain than a regular engine, and it gives the appearance of a "boy racer wannabe". Of course, that's just my opinion. But when you take a car that commonly gets under 20 MPG, and has no power unless you rev it to 9000 RPMs, you've got yourself a useless sports car, that only looks good sitting in your driveway.
The Volvo on the other hand, is one of the better looking cars Volvo has come out with lately. It is safe, reliable, and can comfortably fit 4-5 people in it. Not too mention, when you try to merge onto the highway, you don't have to rev your engine like an airplane just to avoid being rear ended by oncoming traffic. I haven't had the opportunity to drive the Volvo yet, but you should test drive both cars twice, doing so gives you time to reflect on how the car felt, and the second drive you'll notice different things about it that you possibly didn't the first time.
