For me, the biggest one was the security of my future in New Zealand.
A lot can change in 2 years: just because you know now that you'll be eligible for residence via the Accredited Employer pathway does not necessarily mean that you will actually still be eligible for residence after those 2 years are up. Some situations where you might find yourself ineligible:
- The company you work for goes under. You manage to find new employment elsewhere, but your new employer is not accredited, and you only get an Essential Skills Work Visa for the new position.
- You are diagnosed with cancer. It's picked up early enough and successfully treated, but due to the possibility of a relapse, INZ declines your residency application on health grounds. (I know of a similar situation actually happening; the couple affected had no choice but to leave New Zealand and return to their original country as INZ wouldn't even give them new Work Visas.)
- INZ changes the goalposts yet again.
Having a Resident Visa over a Work Visa has its immediate advantages: the right to live, work and study unrestricted as opposed to working only in a certain position for a certain employer gives one an obvious degree of freedom. One also has close to the same set of rights and privileges as a New Zealand citizen (e.g. as a Resident Visa holder physically present in New Zealand for over a year, I was eligible to participate in the recent local government elections, and vote out the councilors who buggered up Wellington's public transport system!). But for me, personally, the biggest advantage is the security of your future. On a Work Visa (or any other temporary visa), you have limited rights and privileges for a finite time, and if you can't get a new visa when that finite time is up, for any reason whatsoever, you must leave. Holding a Resident Visa allows you to remain in New Zealand indefinitely, as well as granting you additional rights and privileges (some of which I've mentioned above) -- and once you've demonstrated a commitment to New Zealand and obtain a Permanent Resident Visa, "indefinitely" pretty much becomes "permanently".
My partner and I were in a similar situation to you, just about a year ago now. I was in New Zealand on a Visitor Visa ("look, see, decide" trip) when I received an offer of employment from an accredited employer: the Work Visa application immediately went in and, ten days later, I was granted a Talent (Accredited Employer) Work Visa. The offer of employment also gave me enough points to meet the 160 point threshold for the Skilled Migrant Category; as such, my partner and I decided that we weren't waiting 2 years and went for it. INZ (no idea how, given the processing time blowouts this year!) granted us our Resident Visas two months after the application was lodged.
My personal opinion is that, if you are indeed serious about making New Zealand a permanent home, and the opportunity is present to apply for a Resident Visa, you should take it. Don't just hold the door to residency open, force your way through it. One never knows if that door may someday close, with you on the other side and no way to reopen it.