Stretchy wrap (or caboo) from birth, then we got a beco soleil when he was a few months old. I don't think you can go wrong with a stretchy and they are available for as little as ten pounds on Amazon. That gives you time to then find a local sling library/group where you can try lots of slings/carriers before you buy, as most of the more structured carriers are fairly expensive, although once you know what you want you can often get one secondhand. It's a really individual decision, most people love connectas for example, I tried one and hated it!
I didn't get on with the Caboo - I'm petite and there was so much excess fabric plus couldn't get DD's head in a comfy looking position. She didn't like it either! However I loved the Beco Gemini, really comfy and easy.
Caboo for when small then lillebaby but really depends on your body and baby. Get to a sling library once baby is born and they will help you. They took one look at me and my massive baby and handed me the lillebaby to try and it was perfect.
I sold my caboodle, hate stretchy wraps. I can never do it up right and they always feels like they sagged. I bought a more structured buckley wrap from eBay. Can't for the life of me remember the name. It was a highly rated one.
Trying them on at a sling library is a good idea although there aren't any where I live. I used a Manduca with both of mine and love it. Ergobaby is also good. Both of these hold the baby in a safe ergonomic position. Whatever you do please avoid any carrier where a small baby faces outward, it's bad for the spine. Baby should always be in a frogged leg position too, not with the legs dangling which is bad for the hips.
Any sort of stretchy wrap (I prefer a moby rather than close caboo, I like to tie it myself) is ideal. We also have an Ergo baby, which can be used from birth with the insert, but they are more for being out and about (long walks, etc.) rather than around the house. Personally, I can't comfortably sit down in a carrier. And yes, a sling library or meet is a good idea to visit so you can try on different ones, see what you like and get advice on fit and adjustment.
I couldn't get on with the stretch wrap no matter how hard I tried, and i did try. Close caboo much better.
I had a baby bjorn We carrier which I found really good, easy to put on and baby in, and a wider seat Base than other baby bjorn carriers
I tried a manduca which come highly recommended and it was great, if I had someone to help me get it on. The baby bjorn you put it on, secure it then put baby in. The manduca you put baby in and secure at the same time and I just couldn't do it on my own.
Amawrap until about 6 months - they say it can last until 3 years but I found it a bit unstructured once ds was heavy. Very cosy and perfect for wearing around the house and popping ds in and out during the clingy stages.
Ergo is brill from then on but he felt a bit lost in it before 4 months