Booking.com has the best offers for booking hotels worldwide. I also like their transparent booking process, amenities and hotel feature selection. Use their 'deals' to save money.
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Pro Map View
Check out their map feature which provides a great geographical overview of the hotels
Pro Family friendly mode
Switch on family-friendly mode, if you're only looking for hotels for families
Con No OTA hotel comparison
Booking.com is not an online travel agency (OTA) comparison site. If you need a good comparison tool, try HotelsCombined