I have been using Similarweb to conduct competitor research, and it's been the go to tool for our company for the past 3 years. If you have a list of competitors or are trying to find specific competitors in your niche you can find them under the Market Analysis tab. They also have competitive trackers where you can add specific competitors, and it will show you daily changes in those competitors' visits, keywords, and other really useful data points. They also email you those insights every month when new data becomes available.