I'd actually have to go with #3 for the exact same reason it wasn't chosen by Ms Outlaw, I like the darker shadow, it helps make the image more realistic (especially since the tent looks too well lit in #1 and #2 given that the sun is the only source of light). If I had to guess, I would say you used a standard lighting model for #1, global ambiance for #2, and either GI or full blown Radiosity for #3, just a guess though.