One Size - or specific size??

Baby #1 is on the way and I have started researching MCN. I am going to get a few different brands to try them out and see what suits bubs best.

Question - some brands offer one size and others have S,M & L. Is the one size really one size... meaning will it last until bubs is older? Or would you recommend starting with small and working my way up from there?

Any size advice would be great plus any good / bad news stories :p

I'm not the best person to ask, but I have read from the ladies here that sized nappies are better for a better fit. I have only a few sized nappies but mostly OSFA as I have an 18 month old and another on the way and I wanted nappies to do them both. But looking at the ones I do have they would fit from birth to toilet training as they have fold down bits for n/borns and then graduated snaps for bubs getting bigger to eventually just using the nappy as it is when they are full grown. In saying that I am going to use bamboo prefolds (rectangles of soft bamboo fleece folded) with a nappy cover for the first while with the new baby as they will be smaller, and then once baby has put on a kilo or two, use the OSFA nappies. I mostly chose OSFA for financial reasons..

I find the sized nappies are a better fit on both of mine because they are both quite long and slim and suit a narrow crotched nappy. Most of the OSFA all all pretty wide, so it was hard at first with Miss M to get a good fit. Plus her legs were pretty much chicken legs, so leg seal was a problem!!!! The best ones I found were bumg's or hautes on her.
I use mainly OSFA on DS though - and he's 2.5 (nearly) so they really do last under they are toilet trained. However, I do stress that he is 13.5 kg and quite slim - he can still fit into most mediums, so I would expect him to fit into OSFA until he's like 5 or something.. lol

I would go with the sized nappies as well - they are a better fit - in saying that though I do have quite a few Baby beehinds Bamboo (OSFM) and I use them at home as they are more bulky and fit under trackies/one piece suits ok.