Invisibility. Basically, the question to me is which option gives you more additional freedom. Flight is not practical in my line of thinking. For one, Air Traffic Control would get tired of me pretty quick. Also, the government would no doubt be after my butt. However, invisibility grants me the power to take actions that have no consequence. The American Dream stripped down to the basic: power. Pure, blissful power. Of course, I have to be careful: again, if the government gets a hold of me, I’m dead on my feet. So, no peeking about in Fort Knox, or giving the Prez an Atomic Wedgie. No matter how much I’m tempted.
Invisibility every day of the week, and twice on Sundays.
Picture it: You’re a super-powered news flash. The headline in every paper in the world. Scientists want to study you, governments want to recruit/eliminate you, reporters want to interview you, etc etc etc…
Now, with flight, you can get away from these people for a while, but you gotta come back down sometime.
With invisibility, you can actually dodge these annoyances, assuming you even let the world at large know about you in the first place.
Plus, y’know, showers, ladies, etc.
[sub]Although, just spying on women in the shower is pretty boring. I think most invisible guys would end up being called “The Phantom Groper.”[/sub]
A simul-thought simul-post.
Nifty.
Invisibility. No question.
Fighting crime, in unique ways, plus the ability to fulfil my voyeur streak without trying to talk my girl into taking a camera into the locker room.
Hehehehehe…
I already have a pilot’s license, so I’ll take invisibility. Then I can be invisible while flying my plane - that’ll freak out the ramp attendants!
Invisibility. And I’d use it to fight crime. Really. Er…you don’t believe me, do you?
Okay, I’d really use it to freak people out. Opening and closing doors, moving stuff around, moaning like a ghost, etc.
Invisibility, no question.
One of the things I’d do is sneak into the White House and eavesdrop to figure out what, exactly and precisely, is motivating Bush to self-destructively pursue his stupid war.
So in a sense I guess you could say I would in fact be fighting crime. 
Flight - can you imagine how brief your life would be with invisibillity?
- Crossing roads
- Getting in the way of people who say “Just test fire it over there where it can’t hurt anyone”
- Getting hit by people once they realise that you’re the invisible guy perving in the women’s showers.
Though flying while invisible would be the best bet, invisibility it is. Worlds of work would open up, nevermind, um… other stuff.
Oh, definitely flying!
Practical? The flying I do NOW isn’t “practical”! What does practical have to do with this?
Never lost? Ha-ha-ha… Most people a couple thousand feet up get quite lost. After awhile you get re-oriented but it’s still hard to read the street signs from up there - they’re at the wrong angle and kind of far away to see clearly. GPS is your friend
Just watch out for that ADIZ “no fly” zone around DC and Baltimore, OK? You’ll want to come in low and slow to avoid the radar. Watch out for an F-16 on your tail.
Anything that lets you fly that weighs either less than 254 lbs (with engine power) or 156 lbs (without engine power) does not require a license. So watch your weight and you won’t have to deal with license requirements 
Actually, pilot weight doesn’t count.
I’d be more worried about the government being after my butt. Air Traffic is no big deal - carry a handheld transceiver and talk nice to them, they’re no problem.
If I actually HAD this power I’d probably keep it a secret - fly only in way out of the way places. Take up hang gliding - I’d be doing the flying, the kite strapped to my back would be just camoflage. Stop worry about whether or not I should invest in a parachute. Take up sky-diving, but without the worry of sudden death by impact. Stuff like that.
Would also make changing lightbulbs much easier…
Invisibility. Flying just doesn’t do it for me. I manage to get to the places I want to go without too much trouble.
I like the idea of invisibility not so much in order to watch other people, but to be able to do whatever I like without other people watching me. I also like the feeling of power – you could really could control other people if you knew all of their secrets.
Damn it. I didn’t think of that. Not to mention cleaning the gutters, sweeping the roof, getting the cat out of the tree … I have to rethink it now. Curse you.
If I could be invisible, I wouldn’t even bother to live at my house anymore.
Flight. Catching birds would no longer be a passive mist-net experience.
Invisibility. I got nowhere to go, flying or driving.
Ultralight aircraft must still abide by FAA regulations even though they do not require a license.
Yes, but as long as you stay outside of airspace requiring a radio, and don’t start posing a hazard to anyone else you’re pretty much OK. Radios are only required around big airports and above 18,000 feet. Since you by yourself aren’t going to generate much of a radar return they’re unlikely to catch you if you did cheat, unless you went >splat< on someone’s windshield.
Unless you want me to regurgitate Part 103 and the relevant parts of Part 91…?
Invisibility, of course.
Steal all the money you want, at will.
Go to the IRS building, change their records retroactively to reflect the money as “earnings”.
Sneak onto planes, visit the world, sneak into political meetings to see what really happens, ditto White House situation room, Pentagon, Saddam Hussein, Israeli cabinet.
Of course, biggest way to “legitimately” earn money is by using “insider” information in stock trading.
just to be a little more exact Hiesenburg IIRC said the very act of observing an electron changes it. Same applies to people, if they know they’re being watched then they act differently.
oh, and definitely invisiblity.