Welcome aboard Cruise Mates! Nice to have you here. You'll get alot of great information from some great people, so jump right in and ask away.
Cruising is definitely one of those things where there's something for everyone no matter their taste, budget, or lifestyle. And you'll get as many recommendations as there are people about which one is best for you.
But as I always say, what one person loves another will hate, so it's very important for you to find the right one for you and not the right one for them.
First, it's really important for you to work with a reputable cruise specialist who can provide as much information as you can handle so you can make the best decision for you based on your budget, lifestyle, and requirements.
Now, with all that said, based on what you've provided so far, I would personally suggest you take a good look at Princess, Holland America, and Celebrity. We've been on all of them several times and love each of them for different reasons. We're a little older than you (63), but we prefer the more relaxed style cruises with less children and, of course, really good food! And we prefer the smaller ships over the mega ships. But that's us, you may be completely different and may want more amenities, in which case you may also want to look at RCCL, NCL, or Carnival. That's why you really need to talk with a specialist - they can be a wealth of information and their services are free to use.
Your first cruise is something special, so make it something really special!