My family all lives more than one plane ride away so I've done my share of traveling. I agree that a carseat is easier if they'll sleep. One idea for a two-year-old is how long are her legs. A couple times we took my daughter and her legs were not long enough to bend at the knee over the edge but were long enough to just keep kicking the seat in front of her. It drove us mad to try and keep her from disturbing the person in front of her. The only other problem we noticed is that you have to attach the carseat via seatbelt on an airplane, and on our seat the buckle was tightened and sat squarely in the middle of the seat, which bothered our daughter's back (it was square in the middle of her back). That didn't bother her until closer to three though (I think) so at 3.5 yrs we started going without anything. Wouldn't do it at two, though. I always liked the safety of "She's all strapped in and won't jump away if I fall asleep" or "She's old enough to listen and obey (or be disciplined) and might fall asleep if she could just put up the arm rest and set her head on my lap." Anyway, think through your trip, if you have help or it's just you (I've done across the country with just me, the 3.5 year-old and the nursing 7 month-old... yeah, I'm crazy), and what do you need for the car at your destination. If you are already taking a stroller then you don't need an attachment to roll or carry a seat of some kind, but we also have a separate seat that attaches to a carry-on-sized rolling luggage. It was designed by a mother and flight attendant, and there is head rest that also pulls up and flips over to become a tray. With just one kiddo (or just one who needs to be "carted") it was pretty great. Plus our daughter thought it was the coolest thing ever. It's upstairs tucked away but if you want more info just message me and go look up the name and website. The cool thing about it is that it folds up on top of the luggage but still fits in the overhead compartment. Brilliant. If you are going to check her car seat (and have the booster just for the plane, for example) I would invest in a carseat cover bag. I knnw the Britax's are large, so make sure you read some online reviews before you get one. The best part about a carseat bag is that it has to be big enough for the seat, but there's no kid in it. This means that for us, bulky jackets we want to have upon arrival but don't want in the airport go in, or extra diapers, or whatever needs to be easily found but checked (or just overflow). Okay, this is turning out to be less about the carseat/booster question, but all these ideas have helped to think through the options for travel for our family, at least. I think looking at your flight times, assessing your daughter's schedule and likely behavior, then looking at your needs and priorities (checked bag numbers needed - like do you need her ticket to have a pack-n-play and her clothes bag and you need both your bags) are all factors for each trip. If you are going to have a stroller for the airport, consider one with an under basket that could maybe hold your booster seat (hard to imagine that carseat would fit). I've found the larger stroller, since I gatecheck it anyway, let's me take more off the back but only fits certain items certain ways. It's still usually a plus over an umbrella stroller, however. When I went with both girls and just me, I actually packed up and tested bags for angles and ease of grabbing for the double stroller basket size and shape. Let me know if you want any more info!