Nepals are pretty much the standard boot for NZ summers. You'll see heaps of them in the huts, and they do the job very well.
The Mont Blancs are Scarpas latest attempt to try and capture some of the market back from La Sportiva, as such, they've pretty much copied the Nepal. They're very similar boots, with the Scarpas being slightly lighter, which is always a good thing.
However, as usual, it depends. Try them both on, and buy whichever fits better. For me, I find the Nepals have a slightly straighter last (good for my wide square foot) and feel like a wider toe box too, so I really like them. If you have skinny feet, it might be a different story however.
One boot that I saw a few pairs of around the traps in both NZ and Canada are the La Sportiva Trango Extreme Evo GTX. I found the fit was much more like the Scarpa last, but they are super light for such a stiff boot and everyone who was wearing them was truly raving about them. If you can try some of them on, they'd be worth considering. It'd be a case of saving the weight vs having a less durable and less warm boot. It's a big weight saving though.