Normally I automatically say Land. But you have up to a month with is wonderful. You could do a little of both to save moving around so much. You could either fly to Honolulu and do Pride of America which as long as you lower your cruise expectations a tad...ok more than a tad... it's a fantastic way to get an overview of Hawaii, it also does the afternoon cruise by the Na Pali coast and an evening sail by the Volcano.
You could also fly into Vancouver and spend a couple of days to break up the flight and do a one way sail to Hawaii. They do those in September after Alaska...or other way around in May.
Or, you could just do a straight up land trip, moving between the islands isn't too bad, especially with a month