1. - 3.:
tcsh for user, csh for root.
also on 14
I neither have the will nor see the need to change, cause I'm used to those for many years,
can do everything I need to do with a shell (except scripting), have my configured .cshrc and history for many years, am used to its UI and syntax, and would be pissed if I'm forced to change.
Under sh/bash most things are not only differet but seem a bit more complex, and complicated to me.
If I'm "accidently" in a bash I get pissed in no time, just because I'm not used to its behaviour, and I'm not willing to learn it, as long as I can use (t)csh.
I don't see why to use a more complicated way, or even change it for no reason, when all I need can be done with the tools I already have and am used to.
My .cshrc has 123 lines - at the moment; besides my wm .config it's one of those config files I edit regulary to fit my needs.
It's the original default one I modified:
the aliases for ls, pager, and editor, the prompt, and added several aliases myself.
If I'd take a peek to another shell I was interested in zsh.
Except scripting:
All my shell-scripts have a shebang to use sh/bash, of course.
When I started to learn scripting I tried the obvious: scripting in csh - bad idea (at least to me.)
Learning to script in sh/bash can also be a real brain teaser, because of its special syntax you may not be used to by any programming language you may learned so far, different ways of quoting, and other things (look out for the differences of sh and bash; traps).
But in my eyes I cannot see a real purpose for preferring scripting in csh over in sh/bash.
I'm sure there are users doing scripting in csh, but personally I don't know one.
4. I don't really know; I presume "Linux-world" won, cause there bash is standard. NO!! just kidding!
sh is the new root (login) shell on 14, not bash, I know.
As far as I know historically sh is the orignal unix-shell.
5. As I said, for (AT&T) unix it's sh, but for BSD it's csh, as far as I know.