[euyyn]

Most asteroids' orbits have the same characteristics as those of planets.

The problem I would see is finding a big enough NEO asteroid, that you actually can stand on instead of floating by its side, or having to worry about reaching escape velocity if you jump strongly enough.

If one's willing to go to any asteroid, not just NEO, then Ceres could be a possibility. A quick search says the delta-v required to reach it from LEO is about half that to reach Mars' surface.

[Roboprog]

I was thinking that having a few feet of gravel between you and radiation would be useful for a base, as well as the ease of coming and going from a smaller body.

I suppose it would be helpful to build some kind of centrifuge in any base to simulate gravity, as well.