Power input selector and regulator design improvement suggestions
Whenever you're thinking about fuses, it's useful to answer the question, "What are we protecting?"  

With that in mind, I think I'd be inclined to separately fuse each of the two inputs and omit the one that's currently (if you'll pardon the pun!) shown.  The reasoning is that it's reasonable to assume that each of those supplies could be capable of supplying considerable energy, so a short within your circuit could cause the wiring between your circuit and the supply to get very hot -- hot enough to start a fire.

With the original arrangement, the fuse would do nothing for that situation.  

I'd also be inclined to move the fuse to just the Vunreg output just in case it might accidentally become the voltage input to the regulators.  This would depend on what you're going to be connecting on that line.  If it were, say, just a panel voltmeter, I probably wouldn't bother.