Being we take car service to the airport from home, we need to take the seat with us anyway. As was mentioned above, it's great, because it keeps them confined to the airplane seat. My daughter is used to it for the car, so it worked well. The one thing I would suggest, depending on how your airport is for on-time departures, don't make him get into it until right before you start taxiing. We leave out of Newark and sometimes we are on the plane 45 minutes before it moves, and that can be trouble. I can save myself 45 minutes of "out, out" until we start moving and then she is in her glory seeing the clouds.
As for a stroller, how long are you staying? I found taking my 4 yearold godson that it was better for him with a double stroller (the singles can be small) and it gives you a place to hold some of your bags. However, that was when I was single and didn't mind paying the $16 or so a day. Now, we take the Graco Lite-Rider stroller from Wal-Mart and Babies-R-Us. For $50 or so, we are going on our 3rd trip with it, not to mention use it daily during the spring, summer and early fall each year for walks around town here. PLUS - my daughter walks through or is carried through the airport. We pile the carryons and the carseat on the carriage and it's great!
Best of luck and enjoy!