I looove puppias, it's what we use daily! I was always told they run small, but i haven't compared it to any other similar styles to comment on that really.
I got my 7.5 lb girl a S, my 11 lb boy, a M and my 15 lb lhasa a M also. McKenzie's neck is too thin but she would be an XS at 4.5 lbs.
They also have step in styles for those w/a small neck. I've ordered one for Kenzie but it isn't in yet
