I'm spinning up some new servers and I'm tempted to make the leap to 13.04 solely because I can install php5 without a PPA. It's not a big deal, it's just a thought.
I've been using 12.04 for about a year now, it's served me quite well and I learned a lot on it.
I'm not worried about LTS, these servers will probably be replaced with bigger ones, rotated out, re-configured and re-created a few times a year.
I use only the remote shell to control the things, so Unity is a zero factor, I know that's a controversy these days so I figured I'd mention it doesn't matter here.
My stack is nginx, php5, and mongodb. I also use server side v8js in a few small places... if that is of any relevance.
Are there any other differences I should be aware of? My first reaction was "No big deal, newer is better, shouldn't make a difference" - but I can't find a clear answer anywhere that isn't related to UI.