What do i look for in web space?

I wanna buy a box and i wanna know what to look for. I know all about connection speed etc but nothing about the software.

As an expreienced web developer / professional what software do you look for in a web box?

What os do you prefer? RedHat Linux or Windows.

What version of RedHat Linux is the best?

What software should you have?
What is Ensim Pro?

Thanks alot for your help!

IF you know of any place where i can get a very good dedicated web server please tell me!