As I've decided to learn both scripting and combat I decided that Nexus was just not going to cut what I want or need.
Seeing as Mudlet is not currently out of Beta yet I plan on switching to either Z or CMud, or MUSH

Could you guy name a couple of main differences along with which you prefer and why?

C/Zmud is very intuitive scripting, many possibilities, buttons, ... but slow when you use many triggers/scripts, Cmud is a little buggy with moments, but it is alot better than the first version. I would recommend Cmud over Zmud.

MUSHclient is rather complicated to start out with, many possibilities but not always easy to use, great speed. But there's a clan dedicated to aid people using MUSHclient, so you're not on your own.

Very capable combat/curing systems can be made in all of these clients.

I recommend MUSHclient, mostly because I'm biased It can definitely be complex, but if you join the MUSH clan, you won't be wanting for support by any means. It's an incredibly powerful client, supporting embedded scripting languages like Lua, Ruby, and Python, which means you get the power of those languages (and their libraries). And MUSHclient boasts a large suite of its own functions as well, beginning with Note() and Send(), and moving to such things as WindowCreate() to build miniwindows.

I've never used ZMud, so I can't give a balanced review here.

MUSH is better, by far. Not as easy to get used to but once you do you'll never go back, period. The speed on MUSH for all my scripting during raiding would crawl on zMud when it's just 1 on 1.

MUSH I'd recommend for the speed and lack of bugs. If you don't mind the bugginess and prefer the user-friendliness, and have a fast enough computer zMUD isn't slow with gagging/tons of triggers, then zMUD or CMUD might be a better choice.