Could see how the wide range of offerings today is confusing. From your description, I wouldn't get all caught up in an exact category of bike, such as 26, 650b, 29, Fs, front fork, fat tire this or that. The bike industry has created this illusion that a mountain bike is some rugged capable machine. I like the many new high end trick stuff BUT its far from necessary. An old road bike, with a quality rigid steel fork can be surprisingly excellent.
The basic criteria.
1- comfort
2- weight (pass on anything over 25lbs)
3- quality strong wheels / good tire combo for swift and easy rolling. (You don't need exaggerated knobbies. Just like the old days, larger diameter has proven itself. The industry is making all the hoopla of going away from the 26" to the 'new' 29er yet the 700c has been around forever and the choice of tires in for them surpasses all of them.)
I was just out yesterday in back country exploring little used trails, some of it rutted, washed out gravel, various grades. Slower going pace but busted out a good clip on the hard pack gravel. Circa 1972 steel lugged bike, weighing 22 lbs, downtube mounted friction shifters, toe clips, 700c X 34c cyclocross tires.
A plush ride but I suppose one could rig to whatever suits yourself such as a flatbar and different shifters, whatever.
For the gravel and smoother single tracks, I'm fairly quick, often leaving guys behind on their fancy suspended 29er's. However they easily get me dropping on the descents but over the long haul, a simple quality old road bike set-up will work for almost all your needs.
Check out Roger De Vlaeminck cyclocross champ~ old school >
And here's one much further back - the 1930's
