The orange one feels too Photo-Shop-y. The font choice, layout, and color scheme say planetary invasion zombie apocalypse to me.
I like the retro-feel and composition of the not-orange one better. It feels more inviting.
The font choice and layout is a bit off the mark, especially the green.
The "Humorous Science Fiction Novel by" needs to go. It's too small to read in thumbnail. If you have to say it on the cover, the cover isn't working.
JMO.