I am one for not ditching the dash tweeters and just running a coaxial in the door, first off your loosing a lot of sound stage by having all the audio coming from your feet. Second it never sounds as good as having a separate tweeter as some have found out by doing that and have went with components after the fact. My recommendation is to go with a good set of components and do it right the first time. Polks are a great budget speakers hence why they are recommended however if you want something better hertz or focal even rockford fosgate has some nice units. As i have become a dealer for ARC audio I have been recommending them more and more as I like there clean simple products that have a great sound for the price.

i use polks cause they sound natural, are reliable, and they fit. it's user friendly.
budget wise a couple hundred bucks give or take a grand do not make much of a difference to me.