I've never booked on vacationstogo (my in-laws had a not-great experience about a decade ago - I know everyone has blips, but subjectively I'm no longer interested in them as an agent) BUT they have the best schedule/database I've found online. They also have a newsletter for singles - cruises with small or no single supplement. I do all my own planning but typically book with a travel agent for the perks.

For us - we cruise to see where we might want to visit more on land in the future, and also to see things best/only seen by ship. I want a small ship (<1000 passengers, preferably closer to 600) because I don't care about nightlife or being entertained, and I don't like people. Though we started out cruising old/smaller HAL ships, then R-class on Princess, these days the small ships are all luxury brands. So when we do cruise, drinks & tips & internet are included in the fare. So choose among all the variables, and when you are comparing fares- make sure to compare inclusions/exclusions as best you can.