What you buy may depend on what type of network you plan on having. You need to make sure that the card has a connector for the type of cable you are using. You can't connect UTP cable into a BNC connector. A BNC connector is used for Thinnet cable. Likewise, Thinnet cable can't be plugged into a RJ-45 connector.
Some cards come with both types of connectors.
Also, some cards are for use with only specific types of networks. If a card is NE2000 compatible, then it should be good for just about any network. The card should also be 16-bit.