The FULL variant is a writable and configurable NDEF tag with optional advanced features such as media-dependent access control and write-once support. It can be configured during installation and at build time. By default it will be a writable NDEF tag with 256 bytes of memory. Its load file size ranges from about 1k to 2k bytes depending on selected features.
The TINY variant is a minimal read-only NDEF tag that can be initialized by providing NDEF data as applet data during installation. This version of the applet has a load file size less than 1k bytes and is recommended for serving static content, such as a simple URL. Content size is limited to allowable install data (~200 bytes).
The STUB variant is an applet that uses a service in another applet to generate its contents. This can be used for creating dynamic NDEF tags while keeping your actual application applet under its own proper AID. Writing is not supported because it is not relevant and/or convenient for any use-cases I could think of. Load file size is slightly above 1k bytes. You will have to provide your own backend applet and generate your own NDEF data.
If you need to create a new variant it is recommended to start with the FULL variant as it contains every available feature except for the service feature of the STUB variant.