Ok, a lot of guys (and gals) here will vote for polks. However, as a biased owner of SPS-171A's, I can swear by Alpines. Yes I didn't have the pleasure of listening to Polks, but the clear crisp output of the Alpines keeps me a happy customer. I use them for mid and tweet only though.
On a logical side note, Polk's higher RMS capability with a wider band may make it more versatile. Beware though, there is no such thing as master of every thing in the real world.
I also own a set of front and rear IAP adaptors for both front and back. Although they are cut and painted first rate, and their holes match pretty close, in the end they are just MDF pieces that you can cut all by yourself (or have it cut by a pro for dime and nickels). The fronts were still thin for the SPS-171A's, so I had to use the adaptors that came with the speakers on top of IAP's. Also the rear ones are intended to be just templates (as stated in the manual), and you still need to drill holes on your rear doors with the supplied self drilling screws.
What ever you choose, I hope you will enjoy them.
Edit: Not to be hypocratical, the goods, service and delivery were first rate and painless w/ IAP even at a distance of 7000 miles, and I really appriciated it.
Listen to us, try boston acoustic out, they are some of the best sounding, and cripsest sounding ever. I listen to alot of heavy music like slipknot, and mudvayne, but other music too like incubus, tool, etc. And it is an awesome speaker. It also has a perfect amount of bass too if youre into rap.