>>817833there's really no such thing as an all purpose bike, just like there's no all purpose car- they all have advantages and disadvantages which become pronounced or quieted by the terrain/task at hand.
That said, I'm guilty of having once owned 14 bikes at a time. Only two were nice, the rest garbage/beginner tier but THEY ALL HAD A SPECIAL PURPOSE. I finally wisened up and sold/gave away most of them and am much happier.
To me, the swiss army knife of bikes would be a steel 29"/700c disc brake bike with enough braze ons/attachment points for fenders AND racks, front and back. I'd go with a cyclocross geometry over anything else personally. It'd be ideal for road riding of any variety and comfortable enough to tour. It could also handle single track, and easier mountain/dirt applications. Could I rock a terrain park? No. Could I downhill? No. Could I race track or even dream of holding someone's wheel in a peloton? Nope.
If you were to travel to another country (especially 3rd world/undeveloped areas) go with 26" as it's ubiquitous around the world. Also go with cantilever brakes- they're the easiest to rig/find parts for. You could possibly cut a bit of tire to use for a brake pad if needed. Discs are just so nice, esp with extra weight of touring.
Don't know the current state of forks, but last time I checked, locking suspension forks didn't lock as well as I wanted them to. It's also just another thing to break. I love the feel of a rigid mountain bike too, so bear that in mind.
Handlebars are such a preference thing, I'll leave it at that.
