Star*

I like the ideas of 3, 4, and 5 myself. I'm not so sure about second, but that might just be because I tried writting an essay about places I've been to and things I've done there (which was important to me because I did a lot of study abroad things), and I had trouble making it work... just make sure that the essay you settle on tells the reader about yourself, above all else.

I have to say my favourite is e = c / a (what can I say, I like a good math pun ), and I think that would work really well for MIT's optional essay (among others).

DCforMe

#4 seems the safest. All the other ones could end up doing really well if you're exceptionally confident in your abilities, but otherwise, a lot of them sound like they could fall flat on their face. Although #3 does seem somewhat less risky than the other three.