I personally preferred the NXT car wash to GC - but then again i'm currently working my way through a 5L bottle of simoniz wash n wax that cost about a fiver in Costco and it works a treat too :)
Again NXT tech wax is better IMHO - however theres not much between them.
As a top coat to the NXT i'd recommend Megs #16 Mirror Glaze - it's a pure carnuba so you can build it up in layers for a deeper gloss and longer lasting protection.
Other good products would be Klasse All in One instead of the NXT tech wax and P21S instead of #16 - KenL, Scottiecoop and Macblob have used these to good effect recently.