Is 2fort the best map for spy-ing?

In my opinoin it is 2fort. The snipers are allways in the same place and easy to get to. The small bridge makes it easier to backstab because it is a bottleneck. You can jump into the water for an escape. The small rooms and hallways are ideal for backstabbing. The sewers are also good backstabbing places, and a great way to get around. You can go from your fort to the other team's fort without running out of or using all of your cloak. After backstabbing a few snipers you can jump down without getting any damage. When someone gets into your base it's usualy either a heavy, which is an easy kill, once they start shooting, or a scout. The later of the two isn't that great but not too big a threat to you. Though I did see a scout beat a fully healed heavy to death with his baseball bat...

2fort is also where I have my highest score. I killed two snipers then jumped down and, in mid air, backstabbed a soldier, then an engineer who was standing in the corner, but I didn't notice his sentry and it hit me with a rocket. But I got revenge on it the next round.

Are you saying Valve maps or all?  I find badlands to be fun as a spy

Just Valve maps. I don't think I have tried badlands yet, but I will. The reason I usually don't join non-valve maps is because some custom maps are very very biased toward one class.

are you playing on TF2F servers??  We run alot of vilepickle's maps which are great.  Maps like Mach4, Turbine, Choas, Stag, etc... I think Labor is pretty decent for spy as well..

Spy on goldrush is just ridiculous. All you have to do is get behind the cart when the offense is pushing and it's like a guaranteed 3-4 backstabs.

Certain areas are easier than others... some are tight and if offense is spamming then it's difficult to get behind them

Dustbowl defense. Nothing better for a spy.
2fort is easy if the other team is attacking. If they are turtling in their base the spy approaches uselessness.

I always turn around and look in Gold Rush.

Gold rush is in my opinion not too great for spying because there are normally people running behind to join the bombcart but 2fort is just about perfect if you can spy well  enough.

I agree about 2fort being great for spies but goldrush is also amazing for spies.  An offensive spy will have a harder time on all stages than a defensive spy.  I say this because the offensive spy has to pass through the defense to get behind them until the cart has reached certain checkpoints.  However on stage three, the offensive spy has an advantage once the cart reaches the third checkpoint.  This is so because the great that leads to the tunnel opens up and you can get behind the enemy really easy.  This also applies to snipers, if any join the offensive team.