What people are saying here is generally correct overall. If you are using the rpi as a server, the distro ever so barely matters. You probably wouldn't want a gui (why give away half the CPU and a sizable chunk of memory to something you aren't even going to look at?) and every distro out there has exactly the same server packages available.

I would install the minimal Raspbian and then add the server applications you want. Also, don't forget you can completely shut off the HDMI for a tiny bit of power savings. If you are going to use https, every little bit counts.

The only reason I actually name a distro when normally I'm hugely agnostic, is because Raspbian is the official distro for Raspberry Pi, and therefor can always be expected to support rpi's various idiosyncrasies.