This may sound like some advert but It is my choice for that amount of money: a super cruise, with either P&O or Princess.
First point, every day is different. Second is my experience with both companies. Third, the range and coverage of their cruises. Fourth, the food, Fifth, balcony cabins. Sixth, so much to do or simply chill out. Seventh, professionalism. Eightth, knowledge. Ninth, that super after cruise feeling when you just want to sit down and book another one. Tenth, the total experience.
Now I could take up acres of space expanding on all the above but that is inappropriate; and I expect there are many others here who could do the same. But here is the killer - pound for pound you will not get better value on any other holiday. Even the expectation after booking is worth the money.