In my limited experience it comes down to the battery life of the devices. As I use a Garmin Edge 810 now as my bike computer, charging "daily" is pretty much a requirement so having power on hand is good. Also like Rifraf I am not that keen on having to hangout in camp kitchens or laundries or wherever recharging devices so again having the dynamo works.

As to solar, I did try a Garmin external battery pack which is a repackaged Powermonkey-eXplorer and found whilst it "worked" it really wasn't that great. Like others, by the time I get to camp it is getting a bit late to rely on solar for charging. Also I tend to tour during our winter months so again less daylight time.

Each to their own of course.

Andrew