Grinders come in all sorts of different sizes, shapes, weights and styles. Even the teeth are different in certain grinders and will grind in different ways. The type of grinder you choose will depend on your needs and your budget, as grinders can range in price from very inexpensive to quite pricey. One needs to assess their needs and decide on which one fits their preferences best.
Regular 2 piece
standard two piece grinders come in a variety of shapes, styles and colours. Commonly grinders are manufactured out of wood metal or acrylic plastic and you can often find a two piece grinder of any variety for quite cheap. Some people prefer a two piece grinder because it doesn't sift any of the finer material out and maintains the potency of your bud however they are often paired with a tray of some kind as you will need to empty the product from your grinder before you can get to smoking.
Three piece grinders are as the name suggests a happy medium between a simple two piece grinder and a more advanced four piece. Three piece grinders are fantastic being that they help maintain potency by not sifting away sought after material, but still offering a space for your product to collect meaning you don't need additional trays or storage jars.
Four piece grinders are great for heavy smokers being that they grind your product, collect it below and sift some of the Keif or Trichromes from your buds and collects them for you. Trichromes are the part of the cannabis plant that store most of the sought after chemicals such as THC or CBD and a four piece grinder allows you to access just the trichromes or keif as we call it once it builds up in the bottom. I often equate the bottom "keif catch" in a four piece grinder to a tax free saving account that only saves you nice big bills.
One of the simplest grinders out there the grinder card works similar to a cheese grater. Basically rub your buds over a the grater and get a decently chopped up bud. Very portable and perfect for those on the go sessions
Electric grinders are wonderful for people who find it difficult operating a standard hand grinder or people who are grinding up such a quantity that a normal grinder just doesn't suffice. however they rarely offer features like keif collection or portability. They range from a basic handheld, to the fancy Otto grinder, which rolls nice cones. Electric grinders are nice for convenience and are getting good grinding weed for those joints.
With all the choices out there we, you have a good selection of different grinders for different uses. Use the knowledge you have gained, and choose one that suits your needs.