Nice idea!

#2 works better from a design perspective - the white contrasts better against your background picture. You might try using one of the purple logos that has a solid white background - this will ensure it stands out against whichever background you use it on :)

My initial idea for stickers was to get some full colour die-cut hexagonal vinyl ones made up:

The text surrounding this can easily be edited to hold a message, or you could just leave one URL and slap thousands of them up in cities over the world and wait for curious individuals to visit it and find out what it's all about ;)