Kaikoura - swim with dolphins and whale watching

Hi everybody!
I just posted something about swimming with dolphins and whale watching, but I wanna share informations about those activities with everyone who is interested in.
I'll go to Grand Explorer reverse on the 18th of december.
Contiki doesn't go to Kaikoura, a very famous city quite close to Christchurch (about 3 hours by coach), where you can have awesome dolphins encounters (4 hours cruise with 2 hours swimming with huge groups of dolphins) and whale watching (3 hours and half cruise). It would be quite difficult to go there for both activities (it is supposed to spend one night there, but I prefere to come back to Christchurch as soon as possible), so I have to choose between the two: swimming with dolphins is a baby's dream, but my husband really wanna see Whales and orchs passing over there exactly in december (what a case?!).
Did anybody go there?
Did anybody go to Bay of Islands' cruise (Contiki's optional) where it is supposed (weather permitting) to swim with dolphins? Is it a good chance to see and swim with dolphins? if so, I wouldn't need to go to Kaikoura for it (just for whales)..
Any help would be appreciate!
Thanks!