My husband and I moved cross-country with our rescue dog Buddy - This was a great pet carrier! Buddy was comfortable, it was easy for me and/or my husband to manage, and United accepted it inside the airplane. We left the top half open during the flight to give him more space and he even got some treats from the flight attendant for "being a good boy" :) 
Buddy is a mixed breed and weighs about 18-20 lbs.