That’s a very open question, so I’m just going to give some options.
We very much enjoyed our recent Celebrity cruise, they have the best food of any ship we’ve been on.
Princess is the best allrounder, we loved doing a transatlantic with Regal Princess.
MSC have the most glamorous ships, but we’ve been disappointed with the food.
Norwegian are modern Scandinavian chic, they have some great ships.
Cunard is classic upper class British luxury if that appeals.
If you wish to push the boat out 😂
Consider something like Silverline, Emerald or Ritz Carlton which are smaller more luxurious ships. We generally don’t do these because they tend not to have theatres on board and have limited choice for food and drink, but a lot of people like the higher crew to guest ratios meaning the service is at a different level.
Star Clippers would be really special they have tall sail ships, a very different experience.
If you want to explore further, Emma Cruises is a great YouTube channel to peruse: