which os do you like best
I like Solaris the best as an OS.
But I use Linux because its more complete as a desktop solution.
Ive always been a big big fan of FreeBSD with its heritage and such, but java doesnt’ work well on that natively, so I use windows for a desktop pc. Soon however, i’ll be enjoying OpenBSD as the code in that is really nice.
As Theo de Raadt pointed out in one of linux’s core source, a comment that said “does this belong here ?”
Nuff said 
if you whant put why you like the os you chose below
Mac OS X.
Because it works.
It has a real shell.
It comes with free development tools for many different languages. (Python, Perl, Ruby, C/C++/Objective-C, Java)
The built-in applications work well together (the mail program and address book and iChat work together and they don’t suck completely)
It looks nice
Application Bundles are a much more sane way to manage application installation.
It’s unix, but it has a UI and most of the idiotic bits are hidden.
The disk structure is more organized so it is more clear where the “right” place is for certain bits of data (e.g. the Application Support folder, /Library, ~/Library),
It isn’t cluttered with crap apps like most Linux distros.
It doesn’t use X Windows, (but it can if you are unfortunate enough to require it)
It has some powerful API frameworks (e.g. CoreXXXXX, Cocoa)