What route order for fate/stay night realta nua?

you don't actually get to pick, the game locks it. Fate first, then Unlimited Blade Works opens up after you finish it, then Heaven's Feel after that. that's also the order the story is written to be read in, each route builds on what you learned in the one before. the only thing to know is you'll hit bad endings along the way, that's normal, the tiger dojo after each one gives a hint for what to do differently.