Expedia UK handles the kind of travel bookings people do every day. Hotels across Europe and beyond, flights from UK airports, car hire for when you land, holiday packages if you want someone else to stitch it together. They've built a reputation as a safe, easy place to book things without too much faffing about. The site works reasonably well on mobile, checkout is straightforward, and if something goes wrong with your booking, there's actually a UK support team to ring.
Their deals section is where they're most useful. Black Friday sales are the obvious time, but they also push last-minute hotel offers throughout the year and seasonal pushes (ski trips in winter, city breaks year-round). The New Year sales tend to be good if you're planning something for later in the year. Hotel deals show up regularly and aren't just five-star nonsense either - plenty of mid-range places get discounted.
One thing worth knowing: Expedia's prices aren't always the lowest. Sometimes you'll find the same hotel cheaper by booking direct or through another site. But their filter system is solid, the deals are genuine, and if you're comparing across flights, hotels and car hire in one go, the bundle prices can be worth it. They're not a specialist, but they do general holiday booking better than most.