And that's true -- there are lot of options. a LOT of options! So you really need to know what is most important to you in a vacation experience -- and where your comfort level is when visiting new cities (English and non-English speaking). The cost of YOUR perfect cruise, and the happiness you have with it, will be dependent upon these factors.
For example -- are you the kind of person who doesn't need, or expects to be, entertained 24-7? Who prefers a quiet place to read over a party by the pool? Wants to dance until sun-up, or greet the sunrise with a few laps on the promenade deck? Has high expectations regarding cuisine options and environments, or is happy with a burger and fries in your cut-offs and tee?
Same thing goes with cabins. Do you have to have as much room in your private space as possible? Do you care if you have a view above your bed? Is it imperative that you have a bathtub? Is physical accessibility a requirement?
Finally, ports of call. If you're in a country where you don't know the language, are you comfortable with striking out on your own with a guidebook and a taxi or tour guide, if that's an option? Will you enjoy the day more if you're within the relative security of a ship-offered shore excursion? Would you rather be someplace you can hike around on foot, or want to/need to travel in comfort from point A to B?
LSH and I can travel on the cheap for three very important reasons:
--> we can go on cruises during 'low season', when inventory is up and demand is down;
--> we're the types who use our cabins for sleeping and showering and not much else; and
--> we gravitate towards ports of call that can be self-driven. Mind you, with proper research and planning, especially in non-English speaking countries, but still 'on our own (mostly so that LSH can spend as much time as he likes photographing things he likes).
We've only sailed three lines (Carnival, Royal Caribbean, and Holland America or HAL). We know that HAL will have a more elegant experience overall, but that the shore excursions will be more sedate or more over our budget. We know that Carnival will have a party going on someplace at any given time, but that the overall experience is somewhat more, um, rugged; however, their interior cabins tend to be larger than other lines, and we haven't done the newer, longer sailings on them.
Royal Caribbean is somewhere in the middle, though I am completely enamoured of the Radiance class of ships -- though LSH finds them 'gaudy' compared to HAL, which just goes to show you that preference is, first and foremost, personal.
We know, regardless of itinerary, that there are many things that factor into any experience on any sailing. But we have different overall expectations on a Carnival sailing than what we would have on a HAL ship. Not necessarily good or bad, just different.
UPDATE: And, as if cruisecritic.com was reading my mind, they just posted a decent summary that might help you decide. Go to http://www.cruisecritic.com/articles.cfm?ID=66.
And finally -- no matter how good or bad things are, they are what you make them. And if you're on vacation on a ship heading to somewhere different or new, it can't be THAT bad, no matter what!