Road bike or hybrid for fitness (also including some commuting and loose gravel)? I'm new to cycling and want to start riding regularly as a form of exercise. I'm mostly going to be riding on roads/pavement but may come into contact with the occasional gravel-isn road https://upload.wikimedia.org/wikipedia/commons/1/1d/Tamsa.JPG

I may use it for commuting 1/5 times but it will mostly be for fitness.
For now I don't see myself riding long distances. I'm not sure what the distance looks like but I would expect 2 hour rides maximum (most days just 45 minutes to an hour). 

I don't want a bike that's too heavy or has too many complicated gears, but I do want one that will hold up well and can accommodate the occasional change in path. 

My previous bike was the cheapest I could find. It was a cruiser and barely lasted a few months when the tire popped after riding over an acorn on the road. So I want a bike where that won't happen again...
Cyclocross or gravel bike.  They both do fine on road.