If you already have pain in your shoulders I would stay with 2 shoulder carriers because they will distribute baby's weight more evenly across your body. Also, the carriers sold here at Attached to Baby are nothing like a Snugli or Bjorn. They are amazingly comfortable because they put the baby in a natural carrying position. I still use my mei tais and wraps to carry my 4 year old daughter.
If you are looking for something with buckles the Ergo carriers is very comfortable and does an excellent job of distributing weight onto your hips. This carrier can be used with a newborn by using an infant insert.
Mei tais are also terrific and can also be used with newborns and/or older toddlers. Mei tais are less structured, so they have a bit more of a learning curve, but less structure = more versatility. Freehand and Babyhawk brands are popular. Attached to Baby will also be selling Kozy (not quite sure when) and I love Kozy - very comfy.
Wraps are super comfortable but take some time to learn. Stretchy wraps are the easiest to work with and there are lots of great ones available on this website (Moby, Gypsy Mama, etc.)
Another aspect to consider is how well you can reach behind you and manipulate the carrier straps and/or fabric. I don't know the extent of your shoulder pain but parents with decreased mobility in their shoulder find it difficult to do a lot of tying and reaching (in which case the Ergo would probably be best for you). If your shoulder pain is just from the weight of the baby mei tais and wraps should be fine.
If you get a mei tai or wrap I would highly recommend purchasing a Tummy to Tummy DVD as well. This DVD is terrific and makes learning how to use your carrier much easier. So look around and see what type of carrier appeals to you. Better yet, you might like to try before you buy. Go to www.nineinnineout.org and see if there is a babywearing organization in your area. The mamas there will be happy to help. And congratulations on the new baby - I think it is terrific you want to carry your little one : - )
M'Liss