In terms of field of view, it's impossible to say because it's entirely reliant on viewing distance. If you're close to the print, a wide angle is natural; if you're across the room, a telephoto is natural.
That said, a "normal" lens, meaning undistorted linear perspective, for full frame is 43mm; for 1.6x crop, maybe 28mm. But generally, 50mm and 35mm, respectively, are referred to as normal, since they're the closest common focal lengths.
Generally, deep focus feels more naturalistic, as the eye has a relatively small aperture and focuses automatically. An out of focus foreground, in particular, can feel very unnatural (which is a good thing if it's what you want, but it seems it isn't). So shooting around f8 or f11 and avoiding really close foreground elements can help make a scene feel more naturalistic since everything will be in acceptable focus most of the time.
You may also want to correct for converging vertical lines (tilt/shift lens) or crop appropriately in photoshop for a more natural feel. The eye automatically makes vertical lines feel straight, and so have painters corrected for this distortion since the Renaissance. (Look at trees and buildings in amateur photos as compared with how they look in paintings to see what I mean.) Lenses don't do this automatically, so you need a tilt/shift lens or post correction (trivially easy in Photoshop, but you lose a little resolution) unless you're shooting straight at the horizon.
So, uh, the most "normal" lens would be the 45mm tilt/shift on full frame, shot for deep focus and corrected perspective. Unfortunately, the normal focal length is also kind of boring at times, or at least difficult to make super exciting. The 50mm f1.8 seems like a good choice, too--natural for full frame and a nice focal length for crop sensors, aesthetically. I actually prefer 50mm on a crop body, even though (or maybe because) it's a little longer than standard.