Ok first question is what your interests are and any must see sites.

If you are used to Carnival, Norwegian and Royal Caribbean will not be culture shock too much with a similar vibe.

I would recommend not booking Costa, MSC or TUI cruises, for that market they are European focused with a different type of service than you’d be expecting, as well as language issues.

A couple warnings:

Some ports are not that close to the cities they claim to serve like Rome (port is Civitavecchia, about an hour from central Rome in good traffic, about the same by rail but the station is a little bit of a walk from the cruise ports), or Venice (many cruises call at Ravenna or Trieste now due to restrictions, Ravenna is about 2 hours south). Other though are very convenient to their cities.

And…

Make sure you know SHIP TIME when you go ashore. They sometimes do not match up with local time so be sure you know what time to be back for.