Done both. For a first time I'd do the land tour. A follow up cruise is fun, but I'd island hop from condo to condo on my first venture. On our cruise this year we re-visited many of our previous visit's destinations and that was nice.
My impression... land in Honolulu, do the Pearl Harbor tour, cruise the Waikiki beach strip on day one, then jump over to the other Islands ASAP. It was pretty much a tourist trap to me.
Fit a luau into your program somewhere. They are kinda hokey, but a fun time.