I don't have a lot of experience with carriers, but I have tried a couple. With my first child I bought a Maya wrap which is the kind with the 2 rings. Essentially, you pull on this long tail of fabric that hangs down in front of you to tighten it. Many people love this kind for various reasons. I didn't. It felt very unstable to me. I've since heard- 5 years later- that some parents of multiples use 2 of these to carry both babies for quite a while and loved that. I never tried this.
My post partum doula suggested trying a Moby Wrap for our twins. It is basically a very long piece of cloth that you wrap around you in various ways. With small twins or preemies you can carry both of them in it for about a month post partum. I bought this and loved it. i did use it a couple of times for carrying both babies but even when they were small it was just too much baby strapped to me! I used it nearly every day for the first 4 months after Ibought it. When Greenbean was colicky, it was one of the only things I could do to stop him from crying. also, it is very comfortable and it was very easy to learn to use. The manual says it can be used til the child is about 2 yo.
We did get a baby bjorn as a gift and whenever we took the babies somewhere I'd wear one in the Moby wrap and DH would use the Baby bjorn. He really liked it. Of course, he never tried anything else.
hth
" I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent." Mahatma Gandhi
"This is the ultimate weakness of violence: It multiplies evil and violence in the universe. It doesn't solve any problems." Martin Luther King, Jr.