We purchased the Snoozer for our 9 lb. PomPoo.  It's not only the perfect size for her, I am impressed with both the versatility and the added features .  The features I like are the side zippered pockets to hold leashes, papers, snacks, etc.  The backpack capability and the ability to hook up to a car seat make this product a good bit more desirable than the competition.

Pros: Lightweight, many uses, added pockets on the sides.  Also it's not too pricey for what you get.
Cons: Haven't come across one yet.