I've had numerous hybrid/endro/ on/off road bikes. IF you are an expert at off road riding and over 6ft tall then purchase a KLR650. If you aren't tall AND an expert I'd recommend a smaller cc engine. Say a 400-500cc for 2 people or 200-400cc for a single person. The problem with larger CC bikes is that off road they can be hard to navigate really rough terrain. A 200cc bike will be able to go highway speeds and be small, light enough to go over some rugged offroad terrain.

I found the KLR 650 had a poor turning radius (for a bike) and it was a little tough to lug around especially when going over hard terrain. On road and on light duty offroad it rocked. The tank was huge and it has a LOT of pep to spare. The only other issue I've found is that liquid cooled engines MUST have a quality rad guard. Personally, I prefer air cooled engines (simpler, no radiator to pop, no fluids to monitor).

These are just my thoughts, take them or leave them.

If you know how to ride a bike I'd get a bike over an ATV any day. Just pack relatively light or have supply drops enroute if you can't.

-Nim