This is why I love the TV show Mythbusters: they routinely demonstrate how our intuition on these matters is wrong.
(A 30-foot fall onto concrete might still kill you, but a 300-foot fall into water will definitely kill you. And if the fall onto concrete doesn't kill you, it will be much easier to get you the medical attention you need if you're not floating in San Francisco Bay).
Huh, I never saw the Mythbusters show. Why would a 300-foot fall into water definitely kill you? I know the world dive record is 172 feet. And terminal velocity for a human is about 120 mph. I imagine if you make yourself flat for most of the fall you could lower that speed and then right before you hit the water take a "pencil" position. Would you not at least have some chance of surviving that?
Water is noncompressible. Maybe the word "definitely" was misused because there's always the possibility for a fluke, but my understanding is that at terminal velocity hitting water is functionally equivalent to hitting concrete.
Look up the "hammer drop" episode of Mythbusters if you want to see the long explanation.
The second point still stands, though. I'd rather fall onto the concrete, where I could get help quickly and if I knocked myself out but survived I wouldn't drown.
In a 300 foot fall, you're not reaching the bottom at terminal velocity. Mythbusters have in fact gone over this a few times and the results are a bit different - falling from such a height onto more or less anything is almost certainly lethal. Given equivalent height, even at terminal velocity, you're still slightly better off falling into water.
You're still going about 80 mph. Just from memory it's roughly 20 mph/second until you hit 4 seconds where it's reduced to 10 mph/second due to air resistance. The greatest chance you'd have is to impact shallow water with mud. This has saved at least three people, of which there are fairly spectacular Youtube videos.
Water is incompressible. So the fall ends up being pretty close to 300 ft. to concrete vs. 30 ft. to concrete. Entering the water toes-first would just mean you have broken legs as well as being dead.
It seems to me the surface tension is the deal-breaker here. When you land feet first, your feet break the surface of the water, which allows for the water to move around the incoming object. You want to minimize distribution of force to only the bottom of the feet.
Of course the force exerted on your feet would more than likely break your ankles and possibly your knees/legs, and severely impinge your hip joint. In addition, your head will likely receive an extreme "punch" as it comes into contact with the water. This alone might be enough to knock someone unconscious or kill them, but it depends on their neck, chest, head, body position, etc.
So if the mythbusters test were done again, it should definitely not be a really fat pig landing on its side; it should be a skinny dummy landing perfectly straight.
I am not a scientist, but I do have experience with cliff diving. (The real trick is when the water level is low, you have to expand your body as soon as you hit the water so you don't shoot down and hit the rocks at the bottom!)
They did some stuff with cliff-style diving too (not quite that high, but it was good enough). That's one of many episodes that convinces me that they play at being more ignorant than they really are in the show, for dramatic purposes; it just isn't plausible that they do enough research to find a guy specialized in high diving, but somehow didn't find out what he could do before he came. I enjoy the show and I enjoy the results, but wish they would be a bit more honest at times, or be a bit more willing to say "Before we start, here's what the 'book' answer to the question is", because it's often obvious they have it. Also, editing makes it hard to tell, but it's pretty clear they very often come prepared with plans B and C to the offsites, again, making it pretty clear that they aren't as surprised that A failed as they play at.
It's the density and incompressibility. When you slap water, it hurts because there is more incompressible water in the way of the water you slap, not because the film on the surface of the water is holding together. Falling into water from some great height is pretty similar to slapping it. A smoother entry dissipates the energy of the fall over a longer period of time, reducing the experienced forces (hence diving).
If you're a diver, or sky diver, or trained you might have the sense to try that, but for the majority your brain is going to be screaming 'oh fuck' when you're half way down.
I'm guessing the correct choice is the concrete, but for some reason I feel like I would still prefer to go for the water...