Because you mentioned "security" specifically I have to agree that BSD is worth considering. I will say that Debian gets the job done for me, but that has a lot to do with the apt sources. 18000 packages, installable in < 1 minute each, is really hard to beat for a n00b! But since you [u]only[/u] want your server to run the few programs you're using to offer services remotely, that probably isn't a big deal for you. Keep the installation as minimal as possible is the right idea for a server.
Also, you said something about going back and forth or alternating among several distributions. If you're installing & re-installing until you find the right one, I suggest adding a separate physical drive, and in the Linux installation step that asks whether to add GRUB/LILO to the MBR, choose no. You'll be prompted to create a bootable floppy disk, which is more convenient while you're deciding which one is best overall, and not that much of a hassle later, since you'll be measuring uptime in months or years, anyway.
Finally, spend $40 on one of these distros accompanied by a manual in a local bookstore. The Debian 3.1 Bible saved me a lot of hassle Googling, and other than exim4 is quite useful for Debian 4.0, also. Without a thorough (not complete, but thorough) reference, the "Linux is too complicated" people almost have a point.