Flying–all the way. Not only could I travel anywhere at no cost with no hassle from airport security but I could also carry stuff so I’d be the elite courier of the gods and would therefore not have to have a day job. Heck, if Superman’s ability to carry other people while flying is a function of flight rather than superstrength then I’d totally have it made–I’d be the coyote’s coyote, heh heh…
Flying
I’d go for flying too. However, that’s based on not wanting invulnerability because then I’d never die. However, if I had a Superman power I might be less inclined to want to shuffle off the earth in due time.
Now my brain is a pretzel. Oh, for superior intelligence!
I think I might have to go for super vision (including the x-ray eyes and laser beam eyes). Too cool.
I was definitely going to pick flight at first. But then I thought about it and realized the best parts of flying like Superman depend on also having invulnerability. Without that you can’t survive supersonic flight (which might itself derive from super-strength), and you can’t fly too high or you’ll freeze/run out of oxygen. I suspect super-vision plays a big part in navigating aerial hazards like birds, aircraft, and other flying supers.
So I’ll have to ask for a dose of that invulnerability, please. Shall I PM you the shipping address? 
I never knew he had super intelligence.
I’d go for the ability to put on a pair of glasses and in doing so completely fool every single human being into thinking I’m someone else.
I’d go for superspeed. I’m intelligent and creative enough that I’ve already got a lifetime’s worth of tasks I wish I could accomplish (books, programs, paintings, etc.) So if I could accomplish those in supertime, I’d finally have a chance to just go and relax at the beach.
No contest: flying.
Endurance.
I always wanted to fly like Superman, so this is a no-brainer for me. Every once in a blue moon when I have a dream of flying, it absolutely rules! Flying would kick ass!
(Now where’d I put my cape…)
(Please be gentle, I was a History major)
I think we’re back to the invulnerability problem here. Superspeed plus physics without super strength or invulnerability… your muscles and bones are going to have a problem with moving a one pound book one foot in .00000002 seconds. It’s the same problem they would have dealing with explosions, except Superman can move much faster than most commercial explosives.
I can rotate my angle grinder’s cutting wheel by hand at 1 rpm while holding it against my other hand and feel no ill effects. At its running speed of 11,000 rpm I’m missing digits.
Stubbing your toe hurts. Imagine doing it at 60 miles per hour. 600 mph. 6000 mph. Eventually you’re losing a leg at impact and before it hits the ground the rest of your body is either leaving earth orbit or coming around again to pass it.
Superman kinda has to be multidimensional.
That said, and all respect to Larry Niven’s classic essay, I’m pretty sure I’ve missed the point entirely. I would choose flight. The best part would be watching the local press try to explain the reports.
Invulnerability.
All of the best ones are dependent on invulnerability. I’d have to pick either invulnerability or endurance.
What superior intelligence? He may have had access to superior tech, but dude was no enginerd.
I’ll take the flight, along with whatever is needed to be able to actually survive the flight. It’s got to be comfier than easyjet and I could always UPS my lugagge…
See, I don’t think you need any secondary powers to survive flight. Birds fly all the time without invulnerability or super vision. One need not fly at supersonic speeds or in high Earth orbit to be flying. One might even argue that you need super speed included in the package to make flight seriously dangerous. So long as you’re staying below a thousand feet and maintain speeds slow enough to keep the clothes from burning off you, I don’t think you’d be in any more danger than running around on foot.
Sorry Nava, as Tengu pointed out, in the Silver Age he was a scientist at least close to Luthor’s ability. Having absolute photographic memory and the ability to think at superspeed, along with above average intelligence, means you can get a long way in the physical sciences. (Can you imagine having the entire Morrison and Boyd for organic chem memorized, without even having to open the book? Now do it for every reference book in the world, in any language.) The Byrne reboot in the mid 80s got rid of that, but it was brought back at least partially by Kurt Busiek during the One Year Later storyline. So Super-intelligence counts.
My choice is Invulnerability. As long as I didn’t end up like Emery Schaub anyway.
It’s already fun, you’d just save a lot of time packing your parachute 
As a 38 year old with random aches and pains I would definitely take invulnerability.
I forgot to mention that I want my supereyeballs to be on retractable stalks.
I’ll take flying, but I would trade it for invisibility.
Does invulnerability cover only external stuff, or does it include things that your own body does to you such as autoimmune or anxiety disorders, for example?
I’ll take flying. Given that any flight over 4 hours is the best way to make me want to chew through the straps…