[nathanb]

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.

[glurgh]

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.

[base698]

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.