david pollak, the creator of lift, likes to use ubuntu. (that's enough for me to use it)
I'm running my lift app on an ubuntu tiny instance at almost no cpu utilization. (however i don't receive a lot of traffic yet)
"What I like about the amazon linux is that it is pretty basic and clear. It doesn't come with too much installed, just the absolutely essential - with mean you might have to install a lot of stuff, but you won't have unused crap running just because you forgot to check."
Ubuntu server isn't bloated, it minimal with little preinstalled. i'd argue that the amazon linux ami has more bloat because it comes prepackaged with Amazon EC2 specific software that you probably will never use.
The important stuff you need to install is: nginx, jetty, database(mysql, mongodb, etc). I think you are better off not depending on Amazon specific software.
If it matters to you, I'd highly suggest getting more opinions.
It's a lot nicer(in my opinion) than Putty.