One of the best maps to learn spy? TURBINE. It's where I learned.
Now, I ain't no Zaw or Frisky Dingo, but I can hold my own when we need a bit of spy action. And I learned it all on TURBINE.
Why do I love Turbine for learning spy? ROUTES. There's plenty of routes for a spy to take. There's two hallways to intel, three routes through the vent shafts, and the enemy team is usually pushing through one route (crooked hallway, rolling door, vents), leaving the other two a bit more open to spy work.
And now that enemy dispensers refill your cloak, you can get from your rolling door to the intel room without dropping cloak just by dispenser hopping, usually.
2FORT is horrible for learning spy. All the hallways are narrow, so if a team is rushing through where you are, you're toast. All the good "pause and recharge" spots are known and checked. Actual viable routes are hard to make it through. Not to say it's impossible, but it's a pain to learn there.