Hi,
Personally I couldn't have lived without my Moby wrap. It was SO comfortable, and my baby practically lived in it for the first 4 months or so. With my first baby I had tried a ring sling and hated it- hurt my back, and it never felt very secure, I felt like I always had to support her with a hand. The moby wrap is super secure and really lets you be hands free. It was great with the second baby since we were always out and about with my older one at the park, etc. Baby slept in wrap and i could still play and move all about. Also, my second baby didn;t like being horizontal very much, so the vertical position of the moby was perfect for her. I never really got the hang of nursing her in it though. And it was kind of a pain to take it on and off a lot, so there were many days when I just kept it on even if she wasn't in it. But very comfortable on the back, as I said.
When she got a little bigger, I switched to the ergo which was more comfortable for heavier babies. Still using that sometimes at 22 months! (one my back) I;ve seen people use the ergo with tiny babies, but it doesn' look very secure to me.
About buying vs making- I tried to make my own moby wrap- I figured it was just a long piece of material, right? But unless you get really nice fabric which is pricey anyway, it won't be as comfy as the moby, so you might as well spend it on the real thing. Also I got the moby D, which has a center panel. I found that to be more supportive to baby (less stretching out as the day wore on) it was a little more pricey ($60 I think) but she spent SO much time in it that I felt it was well worth it.
Hope that helps a little. good luck!