If I were going to pick one of those boxes, I would go with the AMD 2100. It looks like the best balance on price/bandwidth/RAM/and storage. I don't think you can seriously look at anything less than 1 GB of RAM with the bandwidth you're already using. I don't know anything about the host's themselves, but I think Ian's ideas are the way to go to find out about them.
I'm sure Jeremy will chime in here with some sound advice.
This post:
https://www.ubbdev.com/forum/showflat...97306#Post97333Offers some sound advise for anyone looking into a dedicated server.