the one that is not good is carrying the baby in front facing outwards, because it puts a lot of stress on the spine.
Soft-structure carriers like Ergo, Beco, Manduca are good, coz baby is supported and the weight is also distributed on your hips instead of your back and shoulders.
Ring slings are also good coz very versatile, can do all sorts of carry but must know how to adjust.
I have been using a Beco Butterfly II since my boy was a few weeks old (got minimum weight limit), before that was using a sarong sling (suitable from newborn). I like the Beco, usually when I strap him in, he auto go sleep mode