I don't think that he can go wrong either way. If I were buying, it would be the Phoenix. I know some guys that have them and have not heard anything bad about them. Just about everyone that I know that has bought a new rig in the last 6 months has bought a Phoenix. I would recommend that he test drives both and picks the one that fits him the best. The Z9s are super nice too.
Get a Phoenix if you can afford it. My tournament partner has a Phoenix and I have a Stratos but only because I cannot afford a Phoenix. They are awesome boats and well designed. The main thing is you do your homework and make sure you get the boat you like and will be comfortable with.
Nitro has a lifetime transferable warrany also. I told him id get the z9 just for the warranty and spending the extra 15k wouldnt get the justice cuz we both work 6-7 days aweek 100 miles apart so we couldnt even meet up after work to get couple hrs in to make it worth it.
Phoenix. I've spent enough time around fiberglass shops to know those two boats aren't even in the same class. Seen several newer z9 with cracks. As a matter of fact, I will never own a bass tracker, grizzly or nitro. To each his own. Good luck!