I think Abel Tasman National Park is one of the better places to do sea kayaking, as the weather is milder. We went with Abel Tasman Kayaks, which was the first kayaking company to be established in New Zealand, so I think they have got it right at this stage. Our guides were good craic as well as being safety conscious. We were really lucky the day we did it, as there were only four people altogether and two guides.
We opted for the one-day tour (NZ$120), which allowed us to get used to kayaking in the calm Southern bay, then stop for lunch at an idyllic beach before going hell for leather along the mad mile (my favourite part) before arriving in Anchorage Bay. We got a water-taxi back to Marahau, where you can have hot showers and drinks and biscuits. You would need to be reasonably fit and, even if you are, your arms and shoulders will be stiff the next day. You don’t have to be particularly skillful – I can’t ski after a week of lessons, but I mastered sea kayaking.
I can’t say it’s the best way to experience Abel Tasman Park, as I have nothing (except a few short strolls) to compare it to, but I can say that it was one of my highlights of New Zealand.