Which do you prefer...........?

I was chatting with a past passenger of mine last week who happened to be looking at a 36 night cruise. We had a bit of a laugh and a joke about how jealous of her I was as I've always wanted to book a really long cruise. Not necessarily a world cruise but something like cruising to the Caribbean and back from Southampton, about a month or so long.
I've never done it though as I just can't afford to take that long off work or spend that long away from home; but it did get me thinking about which option is better, one really long cruise a year or two or three short ones? (Obviously the best option would be two or three long cruises but you'd need a lot of money for that)!