Good ole' BSD vs SysV
http://www.onlamp.com/pub/a/bsd/2004...SD_Basics.html
Truthfully I've never liked the SysV symlink setup, but that's just my preference. (maybe it was from starting with Slackware years ago.

)
I think the only two linux distros I'd use these days are Slackware and Gentoo if I couldn't use FreeBSD. (rc.conf and the ports just work too well)
edit: to answer more of your question, it
seems that more of the Linux distros use the SysV method. I honestly can't remember what AIX uses, but I can check tomorrow.
-r