Infinities are great but are usually power hungry so if you are going to use them with your original headunit, I would reco looking somewhere else.
The Polks are a good choice all around. Try to get the same brand for all around the car for a seamless sound ...
But really, ANY aftermarket speaker is an improvement over factory ones.
I have a full Bose package with sub and all in the Mazda, came part of one of the "packages" and while they are loud and seem "limitless" power wise, I hate freaking Bose, so trebbly and unnatural sounding.