I bought this cute carrier to take my Brussels Griffon to NYC over Christmas.  It was perfect.  I used it as a carry on and not only did it slide underneath the seat in front of me but it stored her bowel and leash on the side for when I needed it.   Very functional with the 2 openings. Highly recommend. 

Pros: 2 openings, side pockets for storage 
Cons: Wish the telescoping handle was longer (I'm 5'7) and while it worked, would have liked it longer