What are the technical differences between truecrypt, bit locker to go and an iron key?

What are the technical differences between truecrypt, bit locker to go and an iron key?

I am looking to get a new USB drive (my old one took an unauthorized vacation) and am looking into how to secure the data on it. Ideally I would like a visible, unencrypted space that may or maynot be bootable then an encrypted area for low security files followed by a second encrypted space for the most secure files.