Which cruise ship to choose?

Again, like cruise lines, not all cruise ships are the same.

For my money, (which I'm loath to part with), I prefer new, big ships.

Why? Cruise ship have changed incredibly over the last ten years. The new ones have been refined to such a degree that a ship of 10-15 years old can seem like there is a 20 year difference. 

Oasis of the Seas - Central Park

I'm not just talking about the absence of new sexy features like out door movie screens, ice skating rinks and surf riders. It's much more basic than that. Ten year old ships have narrow corridors, low ceilings, cramped bars, theatres, buffets and main reception areas. They generally have smaller cabins, atrociously small bathrooms, no all-weather pools and perhaps worst of all slow lifts. 

Cruise ships date very quickly. And when you add in all of the wear and tear they experience in their 27/7, back to back schedules, along with the corrosive effects of salt air, they really should have a 'complete' refurbishment every 3-5 years. (Not just a comestic one).

Rhapsody of the Seas main dining room

Note the word 'complete' - some ships of 15 years if carefully maintained and refurbished every 5 or so years can still offer a beautiful cruising experience. Rhapsody of the Seas is a perfect example. Royal Caribbean don't just change the carpet, they are constantly adding new concepts and restaurants. Rhapsody has good bones and works well.

Dawn Princess main dining room

Princess, at least here in Australia seems to have taken short cuts, replacing carpets and furnishings, but with reproductions of the original designs from 15 years ago. And unlike Rhapsody, the Princess ships do not have good bones, and suffer from poorly designed public areas.

Size. I used to think that a big ship would be hideous. Far too many people. Crowding. But surprisingly having been on a ship with 4,500 people it never felt crowded.

The reason I personally recommend bigger ships for first time cruisers is that they offer so many more options, not just in terms of activities and dining, but loads of different passive areas such as by the numerous pools, initimate bars and open decks.

Small ships have a place and the super elite 6 star ships from all reports are simply sublime, however if you are new to cruising, I'd personally recommend you try a larger one. But that's just me.