This isn't a plastic vs. leather debate, as I know the + and - of both.

Question is which is going to be better suited for a couple months (jan-aprill) climbing around the southern alps? Thinking of going leather with a Vapor Barrier Liner socks to prevent moisture build up in the boot from sweat, but am worried about getting trench foot with having a VBL on so much. Don't really want to go plastics because they are heavier and I plan on being on some rock.

I have both and my buddy just has leathers.

Any advice is much appreciated.

Personally, for that time of year I'd go leathers, and forget about VBL's.

Wear trainers for the long walk-ins and walk-outs (and creek crossings), leaving them buried under rocks at the base of the route or in a hut. Try to wear your leathers only when you hit the glacier, keeping them as dry as possible.

It can get really cold higher up on mountains like Cook, even in summer. So if you're prone to cold feet, consider plastic boots with trainers for the access walks.

most locals would go leathers esp if walking in/out...just more comfy and if you're just going up the linda it's not going to be technical enough to require really stiff boot anyhoo