Moderately long time lurker, first time poster. I just felt compelled to respond to this.
To be completely honest, this thread has given me cause to worry, significantly, about the mental conditions of those online, as well as generally (seems like everything on the internet does this) lower my stock in humanity. Discussing the various disgusting or at the very least, immoral, uses for invisibility, honestly... But, there seems to be a thing you're overlooking. Unless you stay invisable 100% of the time, you may very well get caught, as you leave bits and pieces of yourself wherever you go, whether or not people will notice it at the time. However, when you start the murdering/robbing/whatever, you'll likely get forensic investigation of the scene. And, if you participate in human society whatsoever, this may be tracked back to you. Additionally, breaking into fort knox/whatever isn't near as easy as you all seem to think. Invisible or not, there is still such a thing as a bank vault, infrared sensors, and other various techniques of detecting invisible people (and, yes, I'm sticking to this point. The name of the thread is 'invisibility or flight' not 'undetectability or flight'). And, if the authorities know you are 'invisable' (or, at least, very good at not being seen), they will be significantly less restrained in the methods they use to apprehend you, rather than allow a murderer/rapist/whatever else to continue as a menace to the public.
This brings me nicely to my next point: Publicity. Yes, Flying is much more obvious, but it is also much, much less likely to have you locked away preemptively, because of the near-impossibility it would be to attempt to catch an invisable when induldging in nastier vices or committing other acts that society doesn't usually tolerate, when the same is not true for a flying person. If you could fly, yes, you might frighten some people, but I'd say that you're just as likely to be looked as a quaint trick, a badge of honor for your country, being the only 'super'human on the planet. By contrast, if you had the potential to do an endless list of detrimental things, without most anyone being able to stop you, or even defend themselves, I don't doubt that most 'normals' would think twice about having you locked up for good. And, if they designed somewhere for you to be kept, going invisable wouldn't help, they could just gas you to sleep, then restrain you, as necessary. As such, I would say flight, as, really, I don't have too terribly many inhumane or perverse ideas that I'm too much of a coward to try out as I am. Besides, the travel possibilities of flight are frankly, fantastic, as long as one assumes that it's superman-or-better level flight, regardless of the various impossibilities that'd represent (because you have at least as many with workable invisibility).
Ultimately only my take on it, however.