Ranger Joe, everyone makes a good side by side, but the best is the one that fits not only your budget, but needs. You said, "My father is 70, so this is much more for utility than any sort of sport. I think it would be good if it had some sort of small carrying capacity." So, that could leave out many units. Lloyd is promoting the RHinno 450, which is what I drive. I did drive an older Mule 550, but switched when the Mule 610 came out, because, frankly, it wasn't enough of an improvement over the 550 to justify 6K. So I bought the Rhino 450 for 7K and never looked back. FOr your father the Mule 610 would probably be fine, 400# bed capacity and same towing capacity as the Rhino 450.
If he ever plans to drive across his lawn though, forget the Rhino. It has an all time locked rear end which will damage the lawn, unlike the Mule which can be locked or unlocked in the rear end. The Mule is old school, but so are a lot of 70 year old men who want simplicity, and something that has proven itself over and over for many years. Mule top speed 25 mph governed. Rhino 450 top speed around 40 MPH before the rev limiter kicks in (at least on my 2006 model). Good luck with your purchase.