I suspect we're not really inveterate cruisers. Have loved the PG and really liked the Diamond, but can't really say I would cruise again in Europe, unless it happened to be combined with an interesting land trip, i.e., serendipity. If we go back to Greece, for instance, it won't be on a cruise, I think.
I want to do the Norwegian fjords, but would probably choose Norwegian Coastal Voyages for that, just because it's traditional--for Norwegians it's like taking the train across Canada--something every Canadian's supposed to do in their lifetime (and I haven't.)
I'd also like to do the Panama Canal, and Alaska, but those are both itineraries that Radisson still covers nicely.