Lots of information here but back to the original question from Korimako, will you or anyone else like a particular cruise line? The only reasonable answer is "it depends":
Where you want to go being the most important one. Many cruisers are loyalists to a particular line, there are certainly benefits and perks to that, as well as gaining familiarity to ships, staff and amenities. And there are some general characteristics you will read about if you scroll through the various line specific boards, things that people really like or don't.
Others move around, often based on the itinerary. Some lines have a specialty in an area, Paul Gaugin (part of Ponant) for example in the south pacific. We chatted with a cruise director on Silversea, who had worked on several lines, who was very candid that Silversea did this or that really well, but if you want to go to x, Seabourn (or whoever) does that better.
And as Fletcher points out, there are some places you can only go on the small expedition ships, and yes you will not have some of the things you find on bigger ships.
We are going to Antarctica, the Faulklands and South Georgia island on Ponant next month. You can't do that on Oceania (which I agree has great food). I know that the ship will be smaller and the cabins tighter than what we found on a recent Seabourn Venture polar cruise. We picked Ponant originally because they have a great reputation in the Antarctic region - they have had numerous ships in those waters for years. Other lines do as well for sure, but the French cuisine was a positive! We will go with an open mind and are looking forward to the penguins and spectacular scenery. Which is why you go there anyway. Will let you know how it goes.