Which Linux distyribution should I use for NW6.4 sneak prev.?

I read on the Technology Preview SAP NetWeaver 04 - SAP Web Application Server on Linux website that I need Linux in one of these distributions:

"Any newer Red Hat or SUSE Linux distribution. This TestDrive has been tested to work with SuSE 8.1, SuSE 9.x, Red Hat 9 and Fedora Core 1. Nevertheless also newer versions should work."

I am about to install a new fresh server with Linux on it but I am not sure which distribution is the best.

Also, are they free? Which is the best free Linux distribution that is capable of running NW6.4?

Thanks