We picked the MiFare 1k chip because our prototyping indicated that these chips are the most flexible to start with.
These stickers are a decent size, so it's easy to make a connection with the phone. The size also allows for a decent logo to be printed on the sticker. The 1K chip is also pretty fast, and holds a decent amount of data, which is great for tinkering and multiple read-writes.
This chip cannot be made read-only.
See our collection of Mifare 1K stickers here.