I purchased two in a row.  First, I bought the small.  However my tiny Maltese puppy grew out of it at about 4 pounds.  The small was delivered to my home in Toronto, in a timely manner.

I loved the small so much, but when the pup outgrew it, I then purchased the medium and had it shipped to my daughter in S.C., in the States and picked it up when we visited her for the holidays.  The medium size is PERFECT for my pup, and I can take it on the airplane.  She is just 5 pounds now, and can lie down when the carrier is upright.