What are the best grapes for making Port wine?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
What are the best grapes for making Port wine?
—Berenice G., Vancouver, B.C.
Dear Berenice,
For starters, I want to make sure you understand that most of the time the term “Port” is used, it’s to refer to genuine Port from Portugal. There, more than 80 different grape varieties are authorized for Port production; the most widely used—and highly regarded—are Touriga Nacional, Touriga Francesa, Tinta Roriz (also known as Tempranillo), Tinta Barroca and Tinta Cão.
You may have seen “port” from other regions made with other types of grapes. Some winemakers have borrowed the term to refer to their own fortified wines, but it’s frowned upon (and illegal in some parts of the world) to call a wine "port" if it’s not actual Port, with some exceptions that have been grandfathered in.
—Dr. Vinny