there are only two versions of the Apache http server... 1.3.33 and 2.0.52.
The 2.x line is a major overhaul and has some new features. Most people run the old 1.3.x line just becuase "it works."
I assume what you're really asking is not version/flavor of apache but what version/flavor of unix should suit your needs.
there are a several threads about which unix to use so please take a moment to read thru them all.
Personally, I'm an advocate of FreeBSD (http://www.freebsd.org/
) and would suggest you take a strong look into useing it. It's very easy to admin and plenty of great documentation and help all right on the website for the OS.