We will have three in CDs (really hoping DS1 gets potty trained before that but months of effort has led to zilch
). Anywho, there will for sure be two in CDs, but possily three. It's really not so bad at all, having two in CDs. Up until this baby, we have only used one size and the boys did fine, even as wee little guys. The only thing i dont recommend is using CDs whilist there is meconium. That stuff is HARD to get off. We are just going to use 'sposies until all the mec is all out, then go to CDs, but they have to be CDs that dont go too high near the bellybutton bc of the cord (you could always wait until the cord falls off too). Other than that we've always used CDs and have had few issues. We have a variety of OS brands, but the FuzziBunz has been the best simply bc there is an elastic adjustment in the legs and waist. That has been important with us bc in our other CDs that didn't have that adjustment, usually the legs were too big and that is when a leak could potentially happen. But with the FBs you can adjust. It may take some trial and error, but once you get a good fit they rarely leak.
With that said, this time around we decided to get sized diapers for Macy. (and oh my stinkin gosh are those XS the cutest freaking things on the planet! lol). We got some XS, S, and Mediums. I was really surprised at how much bigger the Smalls are compared to the extra smalls, and even more surprised at how big the Mediums were compared to our one size diapers. If i had to do it over again, i probably would have invested in some XS and Smalls, and only very few (if any) mediums. (at least when it came to the brands that we bought). The Mediums are similar to the one size, except the thing is you cant adjust the thigh elastics bc they dont have any. So i would say for that size the OS would be a slightly better deal, but who knows, maybe i will eat my words since i havn't actually used them yet. I did read a lot of reviews of ppl saying that they didn't ever need Larges bc of the size of the Ms. So i would say if you intend on getting all sizes, i would suggest holding out on the Large. Theres a good chance you may not even need them. I have not personally bought them for this reason.
If you are worried about the logistics of two in CDs, fear not! Its' really not much different than having one in CDs. Granted we run an extra load each week, we had to get another kitchen size trash and wet bag, but otherwise it's really all the same. And depending on what your washer is like you may not have to do a second load. We have a super large washer but we stupidly invested in a HE one and so there is less water (less water and lots of poopy/pee diapers dont mix well!) So we have to do smaller loads, which means more loads (bc there are two) but really i would say it's only increased by a load or two every week and a half, or so.