First and Formost SAFETY! Sorry AKFireMedic But if a plane started coming at you your going to be in a world of hurt I use those chairs to fish with they are hard to get out of ( My fat asd;lr isnt no help but those things are hard to get out of.
If I was going to use a Chair it would be something like a Bar stool something with no sides that you can escape out of.
I do however agree that comfort is important so I would say get a Stool. One field I was at had Saw Horses that a Flier could lean on

P.S I hate sounding like I a preaching here but these planes can Kill I remember a while back a person was killed at a show. He was behind a Safety chain link fence with a overhead spure the RC plane hit the fence and the motor came loose and struck him in the head