I used to drive a Honda Fit, and now a Scion xD..
I would suggest that if you are planning to do things with your dog that would require leaving him/her in the car, like perhaps at a trial or show, that you get a car that has enough space in the back to fit a 500 series crate.
As it goes, my Scion doesn't fit a crate, so I can't leave my CsV in the car by himself for any length of time. He helped me 'remodel' the insides of my Fit once when I did..
you might also look at what anchor points are available in the back. when we shopped for cars, we specifically made my car the 'dog car', (we also have a SUV but OH says dogs are off limited.. ) so it was important for me to have various anchor points in convenient areas - all my dogs ride belted in crash-tested seat harnesses that need them.