I have been a kettle guy since childhood. That's what my dad cooked on, so for me it was established as the gold standard. I learned its capacities and limitations, and my skills developed around its design. Now it's like a muscial instrument I have played all my life. Give me a recipe and I'll make it work on a kettle.
I have had some experience with the wagon-style grills. I rememeber helping a friend of mine from cooking school cater a big party. Obviously it was great to have a huge amount of cooking area, but I was grilling lamb chops and they flared up into an inferno. With no lid, I had no other choice than to move them off to indirect heat. There they didn't sear very well. I'm sticking with the kettle.