Ok we get it Papa Bear, the XP4 is your recommendation for him! Point made...
Now here is my HONEST opinion. I agree, the XP4, amazing all around vehicle, I love mine without a doubt. Its fast, great suspension, and like MOST UTV's these days, will do just about anything you need it to do. However, rear legroom in a RZR for an adult is limited. Riding in the back is not nearly as comfortable as a Teryx4. The Teryx4 has amazing rear leg room and is the most comfortable UTV next to the Commander I have ever driven. If there is one area that Polaris lacks in its driver and passenger comfort and styling. Kawasaki definitely wins out when it comes to interior design and driver / passenger comfort. Can't argue that the XP4 is also confortable for the driver and without a doubt feels like a buggy with its low seating position. The T4 you sit high which for some isn't very ideal. I do tend to lean towards the lower more aggressive seating positions like Polaris RZR's provide.
Another huge plus for Kawi is the Teryx 4's gas mileage. I noticed in my dune ride that I could go further on a tank of gas in a T4 vs. my XP4. And yes I said DUNES! The T4 was the most overachieving duner I have ever driven. What I mean is, the T4 in my mind was not the most desireable duner but in the dunes it did AMAZING. With my paddle tires from STI the thing went everywhere in 2wd, and handled amazing with both 2 and 4 people in it.
For rock crawling and trail riding the T4's wheel base is the perfect length where in my XP4 I tend to lay the belly down and high center much more often. Plus the rear trailing arms take a beating, get banged up, and have a tendency to hang up on rocks. Sure the XP4 gets me everywhere without a doubt, but the T4's stance is PERFECT for rock crawling and trail riding. Not to mention having the power steering in the T4 is a huge plus. Of course my XP4 LE has power steering as well but now you can bring in price. The XP4 LE with Power steering has an MSRP of $19,599 where the LE T4 is only $15,199.00. Thats enough savings to buy you the +6 Funco Long Travel kit I have and now be able to blast through whoop sections like everyone else you may ride with that has more suspension then a stock T4!
In the end you have to weigh your options. Of course those who own and spend money on a Polaris are gonna have their opinions as will those who own and spend money on Kawasaki's. I can tell you unbiasedly that both have strong value in the world of UTV off-roading. But only you can choose whats right for you. I personally love both machines and use both machines. However, I am turning my T4 into the ultimate all around family trail rig while my XP4 will be turned into the ultimate dune and whoop hopper!!!