If I had to limit myself to one bike it would definitely be a road bike. That fits the style of riding I do most, which is similar to yours.

To me the big key is to get the fit right. I like my handlebars to be about 1" or at most 2" lower than the saddle. That's taller than you're likely to manage with a typical road bike fit. I'd suggest looking for a bike like the Trek Pilot or the Specilized Roubaix.