We just took our Britax Boulevard w/ us on the plane and it was fine...we even used it rear facing for our 2yo and didn't have any issues traveling through the airport or installing it on the plane.
That said, the Scenera is a decent option if you feel that the Britax would be too difficult to handle. If you have a taller, forward facing, child a great second seat option would be the Graco Nautilus. It is still a big seat and $150...but it has high harness slots, harnesses to 65lbs and then becomes a high back and a low back booster to 100lbs. You will have that seat until your child outgrows car seats!
Just a couple of options.