Honestly. While the P90 is good, if you want the range of a rifle, stick with either an AUG or a TAR-21 (Tavor).
Between those two, the AUG is your best bet. It has been around for awhile and is tried and true. The V.3 mechbox is solid by design and has MANY parts for it that will let you upgrade it to your hearts content.
The Tavor is relatively new to the airsoft scene. It uses a V.6 mechbox, which is also solid and has spare parts available, but the company that makes it has been known to cut corners on some things. I saw a review that said it was great at first, but as time went on, parts started to fail. They can all be replaced, but the Tar-21 is expensive to begin with at $500 USD = $800 here (give or take).
Your best bet in order to get a gun and play without having to worry about breaking or upgrading would be a TM AUG. If you REALLY want a tavor, be prepared to shell out a lot of money for both the gun, upgrades and gundoc services. Or, wait and see if the company improves the gun.