I think what everyone is trying to say is that you won't notice the rears nearly as much as the fronts because you'll be sitting in the front and because of the acoustics of the car the rears tend to get drowned out. They do make some difference but don't make them your priority. What you should do however is stick to the same brand name of speaker because companies all have different approaches to sound.

I personally put the same speaker (coaxial though) in the rear just because I had the money and I tend to balance with a bit more rear coming through. I put Alpine Type-Rs in the front and rear. My alternative would have been to put Type-Ss in the back. They're one step down from the Type-Rs.