RTW - Which direction is best?
 

I'm booking travel to fly frm London to New Zealand for Christmas - which direction is best? i'm assuming going RTW via Asia then back via the USA is fastest way? does it make any difference to jet lag?

westbound
 

I always find westbound travel easier on the jetlag.

Welcome to FT, both of you!
Flying east is almost always faster. Example: HKG-SFO 11-12 hours while SFO-HKG 14-15 hours.
Given those shorter flying times and the natural (although faster) day to night to day transitions (instead of chasing the sun), I find eastbound is also better for jet lag.

I echo the eastbound sentiment

I have somewhat limited experience (3 times, once Westbound, twice Eastbound) I typically don't experience jet lag - ever on any flight of any distance. The one RTW trip I made Westbound I felt crummy for a couple days. Far from scientific but it was bad enough that I wouldn't consider going that direction again.

Since New Zealand and London are exactly 12 time zones apart, it makes no difference which way you go because the time difference is the same either way. Eastbound will be a shorter flight due to prevailing winds.