* less that 70 TPI. Personally, I don’t find these much use for anything other than the strongest wools. I would not suggest purchasing these.
* 70 - 120ish TPI. These are standard wool cards, which work very well for most fibers.
* 180ish - 200+ TPI. These are cotton/fine fiber/fur cards, which should be used for the finer (ex. merino & alpaca) and especially the shorter (ex. cotton & cashmere) fibers.
Within those general categories, the most important thing is to find the cards that work best for you. Our hands and carding motion are each different. The hand cards that work best for me may be uncomfortable for someone else to use. Hand cards come in a variety of weights, sizes, and shapes. Some are flat backed, some are curved.
Having comfortable cards is much more important than the difference between 72 & 95 TPI.
Try going over to your local LYS or spinning guild to try out the different brands and sizes. I’m sure if you asked some of your local spinners they would be happy to let you try out their cards. We tend to be helpful that way :)
Personally, I prefer Schacht hand cards. Strauch makes nice hand cards as well.
Initially I suggest getting a set of regular wool cards. Those are going to be most versatile, and will work with most fibers. When you step up to the really fine fibers you can always purchase a set of cotton cards.