I would recommend to people if they option, to go to a store that sells CD's and physically touch them and explore the different kinds offered. If you look at them you will get a feeling for what you want to use. Some people like the simplicity of an AIO diaper, no stuffing to be done, no folding needed, you just put it right on baby. Others prefer a pocket diaper so that they can adjust the absorbency of the diaper, especially during night time, nap time, and trips away from home. One of my favorites is the option of prefolds with a cover. Yes it is a little more work to get the prefold folded the correct way then place in the cover then on the baby but I enjoy it plus its the cheapest way to go.
If you use prefolds and covers you will probably want around 2-3 dozen prefolds and about 4-6 covers. If you like snappi fasteners have 2-3 on hand. Also optional items are 6-8 doublers for night time and 12-18 fleece liners to take moisture away from the baby’s bottom.
If you prefer a Pocket Diaper or AIO Diaper you will probably want for babies around 20-30 diapers and for toddlers 15-25 diapers. Doublers for night time and inserts for the pocket diapers.
If you want fitted diapers with covers have about 2-3 dozen fitteds and 3-4 covers on hand.
These are just suggestions and once you get started you will more than likely start buying different types of diapers and have a huge stash in the bedroom to use.
A lot of online stores have the option of doing a Cloth Diaper Trial. This gives you the opportunity to try out the diapers for a couple of weeks and find out what style(s) suits you best. Here are a few good site I have found that offer trials.
Ecobuns - They offer a trial package for $25 dollars. There have three different trial packages you can choose from that are tailored to fit more of what you are interested in.