If you had only one lens on your OMD or other MF3 rig for walking around which lens would it be?

MFT cameras are great to travel with.  With my GH1, I would use something like a Panasonic 14-140 for general photography and carry the 20 mm for low light photos.  That is a small, light and very versatile package.  You could make it even smaller with the Oly 14-150 super zoom, plus the 20.  You could extend your range even more with the Oly 9-18, that lens is so light and small also.

I recommend a superzoom and the 20.  The f1.7 makes a difference in low light, and is a very sharp lens.  I of course do not have an OMD, so good luck on your choice.