Taiwanese can choose from either the 旅行證 (Travel Document) which is a book or 台胞證 (Mainland Travel Permit for Taiwan Residents) which is a card. At least that’s how it used to be, I’m not sure if China still issues the book style Travel Document, anybody know? I guess the main difference is that you can use the Travel Document to visit the UN (which you cannot do with a Taiwan passport), as well as entering China, so it is slightly more useful. Downside would be that it is big and bulky compared to the lightweight card they issue.
From another users thread, it sounds like you can apply for the Travel Document at a Chinese overseas mission, whereas the card can only be applied for from Taiwan.
This user suggests that the Travel Document is used by overseas Taiwanese as they cannot apply for a Mainland Travel Permit for Taiwan Residents without household registration. Has anyone ever done this?