Pure water will not corrode your internals...if it did, it would whether it was 100% or a 50-50 mix. TAP water will corrode them, because of the impurities and minerals in it. If you can, you should use distilled water (which you can get at auto parts stores). The pre-mixed 50-50 solutions use distilled water.
You can run your bike on straight water, but water boils at 212 and freezes at 32. Plus it doesn't do as good a job without the antifreeze.
You'd think straight antifreeze would be better, but ethylene glycol will actually gel at freezing temperatures and I don't believe it transfers heat as well as water.
For some reason, a mix of 30-50% water and the rest coolant seems to do a much better job than either one alone.
If you're worried about what coolant, I'd go with the Prestone "All makes, all colors" stuff.