I would never ever use what you used, ever. Just like with Facebook display pictures, never use something you wouldn't like you boss/parents/relatives/friends to see.
To be honest, I rarely use anything that if people asked what it is I'd have to start with 'Oh, er... well it's from <insert hobby/IP here>'. But that's just because I'm all British and repressed.
Even so, at the moment my phone has this:
But that's because I made it and was more than a bit satisfied with it, so I am going to use it. Plus as someone who wants to be a graphic designer, it helps to be able to quickly show someone a small sample of what I can do.
My current PC background is this:
http://th09.deviantart.net/fs70/PRE/f/2012/202/f/f/high_resolution_tamriel_map__elder_scrolls_series__by_belhene-d581jpg.png
because anyone that comes into my room and will see my PC understands what it is and therefore there is no awkwardness.