story wise, red dead. the story in odyssey is interesting, but compared to a Rockstar game, it doesn't hold up. in terms of gameplay, they're both meaty - but in they're own way. I would compare odyssey to something like the witcher 3 with an emphasis on loot. plus it has all of its DLC released. RDR2 has a huge single player campaign and their multiplayer side, if you're into that sort of thing.
you can't go wrong either way, but if you want non-stop content, then go for odyssey.