Hi, we started off with a Hug a bub (or a cheaper alternative wrap style sling - google it you'll find heaps) which we found a life saver in the first 3 mths however after that she disliked it. We used it facing out and on the hip which was better. We then found the Ergo which I am now in love with.

things to look for -
flexibility facing in, out hip
how easy it is to use
how it distributes weight (2 shoulders are better then one)
ability to breastfeed
good support for babies posture and yours

with DS I used a ring sling and it was great also. The only one I haven't liked so far is the kapoochi just becasue it was hard to kget him out without waking him

HTH :-)