Ground Zeroes is pretty cool, although it's really more of a tech demo for the FOX engine that sets up TPP. TPP is very messy, very unfinished. As a long time player of the franchise I'd say ignore the story in TPP.
Peace Walker is mvp though, and you don't need to have played Portable Ops before playing it. Ops is a side story really that just explores the FOX rebellion that's mentioned in the Snake Eater timeline during the credits