Well, it's mine is the simplest answer. I think it's far better, but then I'm biased. ;)

But seriously, it's easier to just play and find out I think. I don't keep track of what the old mod does now so I can't really tell you what they're missing, but essentially if you liked the stuff I made for the old mod - all the events, species, special mechanics and a good chunk of the ships - then you should like what I've done with New Civilisations.

Why exactly did you split off from the NH team?

The Mechanics are a start, more ships than STNH, there are more races that have their own shipsets. One thing that i have also seen is when you play as Fed, the mebers have only their main planet under control but the system is yours while in STNH they have teir planet and system under their control.

As far a s Mechanics go: You have a science mechanics that allows you to choose what type of weapons, torpedoes, ships you can research. Yes you can add the shipsets of member worlds of your coallition to your own or share your ship designs with them, you have a uniform mechanic where you can choose what uniform you have as you progrees in time.

It also has a few more Empires than STNH. Oh and it has four alternate reality empires, The Borg that managed to Conquer Earth, The Remans that managed to owerthrou their Romulan Masters, The Khanate and The friendly version of Carrdasians.

Both STNH and STNC are greate, i personaly like both, They have their own strengst and weaknesses and have their own uniqness.

far more ship options for the federation.

Yeah the two are rather distinctly different in play "feel". Once I finish conquering the Galaxy as the Kzinti (or not) in STNC I'll give it a serious go in STNH.

I've also noted that STNC performs better than STNH.
Usually in STNH I'd not be able to play very far beyond 2200 as the game would begin to lag and struggle. Where as with STNC I'm able to get to the 2400's before the game starts to slow down a little, but it's still playable.