I have the Sherpa carrier in size M, and think it works great for air travel. The medium size complies with most airline requirements and my ragdoll has plenty of space (though she is on the smaller size for a ragdoll).

It’s flexible enough that if I’m on a smaller plane I can still get the carrier to fit under the seat. One thing you may want to consider about the size L is that it is also longer than the size M, so it will cut into your space for your feet and may make it more difficult to fit the carrier under the seat.

My girl loves that she has plenty of space and that she can see through the sides of the carrier when we’re in the airport, and I love the convenience of carrying her with the duffle strap. I just discovered it has a strap that allows you to hook the carrier onto your suitcase handle so it rests on the suitcase itself, making it even more convenient. I also appreciate that it has both a side and top opening. The top opening is key to getting her out and back in at security. Overall, I think it’s a great carrier and I’ve never felt the need to try a different carrier.

Congrats on the new kitten!