To date, I've owned 6 different pumps. The only one I have left is an 870. Chances are, my next pump will be an 870 as well.
While the 870P is an awesome variant, I would recommend looking into buying an older and very lightly used wingmaster in the EE. Build standards were to higher tolerances 20 years ago (as opposed to the current expresses, etc), and you can probably get it for a third of the price of a new 870P. Use that extra cash to pay for ammunition, cause the distinction between any of the big 5 models won't balance up to the difference alongside a few thousand rounds down range at the beginning of your shooting career.