I voted for Senpai's because first thing I saw was "Robots" and when I looked at the other one I couldn't really tell if there was a robot. Senpai's also has a more "soft" feel to it.
I voted for K0n's because when I first looked at it, I thought "wow its pretty x_x" and pretty is close to beauty I guess. It also demonstrates more aspects of nature (trees, lake, mountain, hills, sky, moon/sun, etc.)
Lunia: Kanairi/Ruriri •ₒ• SOSBrigade •ₒ• Mabinogi: Rakusu (Mari) •ₒ• Vindictus: Lisolette