The one piece of advice that was given to me when looking at pellet grills was paying attention to the PID or control part of the unit. Most, if not all, of the grills mentioned here will have a PID that will maintain temp within a 5 degree variable - almost like your oven.
I have the smaller grill from Smoke Daddy. PelletPro 627. It came with two racks with the upper rack being half sized. I purchased a 2nd full sized rack for the upper level, which they cut down for me, and I can do 6 racks of baby backs at one time. Yet it's not overwhelming big for the smaller cooks. Heats up fast and maintains temp well. Their PID is very reliable and accurate. They even sell, and a lot of guys use their pellet hopper assembly for larger build out such as refrigerator conversions.