flying with a toddler- car seat or not?

Going on a 3.5 hour flight, don't need a car seat once we get there.So, do we bring a car seat on a roller so our 2 year old can sit in the seat on the airplane? Or just bring a stroller and he sits on the airplane seat as is? I keep going back and forth and have access to both. I also have a 6 month old, but she will be in an ergo carrier. TIA! via /r/Parenting http://ift.tt/2eEnkzZ