Who has the most modern fleet?

'Book a cruise with us. Recommend a cruise with us to all your customers, we have the most modern fleet in the world'.
You've got no idea how many times I've heard that from the different reps that come to visit us from the different cruise lines. The only problem is they always seem to have a different definition of what the most modern cruise fleet means.
I can see why so many cruise lines want to be able to advertise this on their promotions as it does sound good, 'The most modern fleet at sea'. But with so many different brands saying the same thing how do you define it?

I've heard the exact same thing from MSC, Celebrity and  P&O just to name a few. If you ask one cruise line it means they quite literally have the newest ships in their fleet. Others say all their cruise ships are new to them, even if it means they've bought them from another cruise line so that the ships themselves may be quite old. Still another explanation I've been given is that 'our decor and style is the most modern and up to date at sea'.
So here's my question for you today.......
What do you consider to be a modern cruise fleet?   Is it the age of the ships themselves? The length of time that a particular cruise line has owned the ships? Or is it something harder to define? Is it an attitude or style on board that makes their ships feel more modern than their competitors? Does it even matter?
I know it's always nice to see a new ship but I'm wondering how important the tag line of youngest fleet really is?

Is it better to go on a brand new ship that no one has ever sailed on before, or do you prefer to let other people work out all the bugs and kinks onboard before you book your cruise?
Let me know here.......

Happy cruising