The Operating System of any server is probably the most important decision you will have to make. You may be limited in choice due to the scripting language your sites run in.
This simply means if you program only in ASP, the best and first choice should be a Windows based server. This is not to say that ports do not exist to run ASP on other servers, but why add a layer of complication to your hosting configuration?
If you like *nix variations, the most popular platforms for hosting are by far :
- Redhat products
- Bsd variations
From a server maintenance perspective, you are going to have to 'up your game' a notch - and learn to become proficient with the basics of the OS you choose. Each has it's advantages, and reading up on your choices is the best thing you can do.
At a minimum, you'll need to become aquainted with command line usage, a text editor such as VI or PICO (used at the command line), and an SSH client. (We use the freely available and reliable PUTTY)