This is in danger of being a useless answer, but its all I've got...
I had a look at SME server quite some years ago (so anything might have changed by now, which is one of the things that makes this answer of so little use) and getting something up and running was simple - almost trivial, you could say, if that description wasn't asking for trouble with anything computer-related), but the trouble was, you got something running, you'd got a command line prompt, what else? At that point, I had no idea what to do if I wanted to install and configure a new service or remove one that was already configured. So, have a close look at the documentation and see whether it seems to give you everything you'll need to make progress, or you'll be in the same situation that I was (of course, you can guess and mess, but that seems to kind-of defeat the point of the no-fuss-no-muss, up-and-running-easily part, and if you are experienced with Linux, your guesses are likely to be better than if you are not).
At least if you go for a general purpose distribution, eg a Red Hat or a RH-alike, you'll know what to do to control services and where to get more info, so which is a win rather depends. And while you do know that you'll have to configure everything yourself, it would also be the case that a search on <tutorial Red Hat service_name> will usually throw up more results than you can shake a stick at.
In the meantime, I also noticed Zentyal, which also seemed quite nice.