Good names mentioned above.
I usually think of holsters in categories based on modes of carry.
Since no one mentioned it:
A recently popular mode (in the last few years) of carry has been hybrid holsters: A kydex shell with a leather backing against your skin. These are usually worn Inside Waist Band (IWB) and some are adjustable for cant. The Kydex shell helps keep the holster mouth open for re-holstering while the leather backing is more comfortable on your skin than just bare polymer - especially where the back of the slide on a semi-auto would dig into your side. These holsters are usually a bit wider than your average holster (they look strange at first) but that's because by using 2 belt clips or loops set wide apart the holster won't start to change angle/rotate on you. they're usually tuck-able too. Very popular these days. Examples: Cross Breed Supertuck Deluxe, Galco King Tuck, Desantis has one (forgot the name), Shielded Holsters (seemed to have a low price and I'm considering one).
For every mode of carry you can find anything from dirt cheap to pretty darn expensive. Even pocket holsters. Sometimes you don't know if it will work for you until you try it. Sometimes the cheap works just fine (pocket holsters especially) and you'll get to know the quirks. Eventually you may end up with a pile of grips and holsters that didn't quite fit the bill - it happens to most shooting folks.
Price is usually a big deal for me. Downsides to cheap cloth/nylon holsters is that to add strength, more material is used and they can become bulky compared to a similar holster of another material. If you don't mind it's no big deal (a range holster, a hiking/backpacking holster) and after trying to carry with it you may find it works/doesn't work. If that is NOT done and material is too thin sometimes such holster can flop around a bit when you're carrying on a belt - that happened to me but on an OLD style cheap uncle Mike's that was oversized for my gun. Another thing you might want to look at when you're looking online (it's hard to tell how it'll work by the pictures) is if there are belt clips - have a look at where the metal clip is. If the holster is molded and has a built-in outline of the gun: how much of the gun is above/below the clip? It'll help show how high the gun will ride when you're carrying it. Top of the metal clip = top of your belt. The best would be to find a picture of your particular gun model IN the holster. My particular leather Don Hume IWB for a revolver rode a bit higher than necessary and dug in to my ribs with the slightest bend and printed more too. What I personally want in an IWB band holster is the pistol grip protruding and nothing but the pistol grip - but it would have to protrude high enough to get a firm firing grip on it before a draw. Some folks ride it even lower with part of the grip below the belt line for deeper carry and they knowingly sacrifice accessibility.
There is sometimes a difference between "plastic" and "kydex" in pop holster vocab (please correct me if I'm wrong folks!). Although both are probably plastics to some degree. My good friend has a fobus paddle holster which was meant to be a range holster and that "plastic/polymer" tended to be very sticky/grippy. You really had to yank on gun hard to get it out - that may have been just his holster- I'm not certain but watch out for that. Kydex is usually a bit less grippy and retention is accomplished a bit more by pressure on certain points of the gun rather than friction. Kydex can usually be user-adjust with a hair dryer.
I'd suggest reading reviews of anything you're seriously considering, and going to a gunstore/gun show with your empty firearm to test a couple out. You have to be able to say "no" though if you need to
God bless!
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