Personally I like a ring sling when starting to carry on my back. I find that with a ring sling it's nice to be able to snug the younger kids up, esp when they are young enough to want to look around and not understand that they could fall.
I have a few picutres of my DD in the sling on my back (sleeping of course)
http://rwhite.photosite.com/~photos/...2752956000.jpg
http://rwhite.photosite.com/~photos/...6304196000.jpg
http://rwhite.photosite.com/~photos/...6304072000.jpg
http://rwhite.photosite.com/~photos/...6304146000.jpg
we currently use a new native pouch. it works becuase dd fills it up so she is still snug without needing to adjust the tightness. she also knows that she can't lean way to one side or try and turn around when she's on my back. she does like to test her limits sometimes though!
OUr secret for getting in it is for DD to put the sling on first, just like she was going to carry someone. Then I sit on the floor in front of her and put my one arm through. she hold onto my neck while I stand up and get everything adjusted.
I tried several times to do the "put them in the front and swing them around back" way and just couldn't get it. No matter how far back I started my rings, they would end up in the center of my chest (very uncomfortable). with the pouch I can make sure that the smile part is under her butt before I put it on. works like a charm.
OPh I should say that I sling both DD (3yrs 40lbs) & my neice (2yrs, 24lbs) and have never dropped them.
Chole