Best carseat for airplane?

We are going to be travelling by plane over the Thanksgiving holiday and want to know what are the best carseats to use. We have bought a ticket for our child who will be approx. 9 months when we fly. By that time she will also need a new carseat because she will have outgrown her infant seat (she is already 15 lbs). Any suggestions for carseats that fit? Thanks!