Depends on what you want to do with it..

for desktop stuff and playing around, linux is the choice for you..


for server's I'd go for openBSD (wich has no X) or FreeBSD or NetBSD

the BSD's are more secure (mostly)

but it all depends on you configuration... fresh out of the box.. I'd go for BSD.
if you do the config manualy.. the difference is too small to measure