Bog standard beach holiday - I use a package operator (jet2, Tui, etc). Narrow down to locations I want to travel to, board options, budget, and save several in the app that I like the look of.
I'll then look at reviews, surrounding areas, etc. They are by far the easiest to book, flights, transfers, and extras can be all sorted on one go. Some of them now also do city breaks and villa holidays as well.
City breaks, DIY Holidays. I'll pick a few locations and go on Sky Scanner for flights. Then I'll find an airbnb or hotel on booking.com in my desired location, using their map features.
If I had to do multiple locations, I'd book the flights, ferries, car hire etc first and then book the accommodation to fit.
I suppose the first question you need to ask is what you all want from the holiday. Beach, pool, city break, sightseeing, hiking, and then narrow down to a few locations.
Eurocamp is also good if you are on a budget and are OK with the ferry and driving abroad, and they have tons of locations.