Ok here's my reasoning for what I choose. It is my opinion and I fully realise that not all will agree with either my reasoning or choices.
1# AirFreight
2# Mount Cook
3# Air Nelson (maybe not at the moment but...)
4# Air National/Vincent/Chats
5# Eagle
6# Airwork
Air Freight: Very good money and reasonable duties (esp for a night freight gig)
Mount Cook: Interesting type and very good conditions. Established, well run operator. I believe they average a 35 hour duty week, with five days off a fortnight?
Air Nelson: Good equipment and an interesting network. Terms and conditions are ok. Would be an even better place to work if they weren't so stretched for staff.
Charter operators: (Nat, Vincent, Chats) Good variety and interesting flying. T's and C's vary quite a bit between these operators so a little unfair to lump them all into one. They do however have similar cultures (within the pilot groups anyway). Not for everyone. Main center basings (AKL{CHATS, NAT}, WLG {VAL, NAT} or CHC {CHATS, NAT}) available for all three operators (Chats do spend a bit of time in the Pacific Islands though). Pilots at all three do also tend to work long hours with a lot of overnights.
Eagle: Only real issue with Eagle for me is potential basings. This is a personal choice. If you don't mind being based in one of the provincial ports then it may rank up the list somewhat. When comparing Conditions as well as pay they are ahead of the likes of National/Vincent.
Airwork: Seem to be somewhat disorganised and old school (are there any female drivers there yet?). Very good money but long back of the clock stuff (even in comparision to Air freight). Not my idea of fun but each to their own.
To be fair, all of the New Zealand regional operators have particular attributes that appeal to different sorts and so much of what is desirable depends on what you want from aviation. While I rank Airwork a definate last, some of the guys I know there love it. A disorganised op's setup and a GA approach to some sides of the operation doesn't detract from the positives as they see them (excellent pay, quiet night skys and the enjoyment of piloting a reasonably demanding aircraft).