I personally don't really like the ones with the legs out. I always think: that can't be good for their spine, especially if they're in there for a long time.
I use Kyjen backpack carrier for Zoey. She's about 5.5 lbs. She loves being in there and sometimes won't get out of the car unless I put the backpack in front of her to let her know her highness will be carried. LOL Here's a picture of what she looks like in it.
http://www.yorkietalk.com/forums/att...y-backpack.jpg