I think if we're talking about starting from scratch, MGSV is a very tough game to replay. It's like a huge RPG where there's just too much timesink to get to the parts you actually want to replay sometimes. But if we're talking about replaying missions as long as the save is still there, MGSV is probably one of the more replayable ones. Maybe not quite MGS1 or MGS3, but I've tried to replay MGS2 and MGS4 several times before, and it's pretty hard for me to get into it. MGS2's camera is too much of a stopgap between MGS1's clear top down view and MGS3 Subsistence's free camera. Feels rigid and annoying to me. Can't go back. MGS4's loading times, endless cutscene skipping, and lack of engaging gameplay after Act 2 really makes it a huge bore too. Peace Walker is pretty replayable initially, but then once I realize there's no one else playing and I can't easily get a friend to join in and do silly shit with me or raid a boss fight, it loses my interest too.
MGS1 is probably perfection when it comes to replayability. It's not as deep a game as MGS3, but it's the perfect length and has nice simple arcade controls and no extra simulation stuff. Also, Rex > Ray.