MyHeritage is my favorite site for genetic deep diving. They don't have the largest user database, but in my opinion they do have the best user interface.
MyHeritage allows you to sort your DNA matches by total centimorgans, number of shared segments, or largest segment (as well as name and match date). While total centimorgans are the best indication of close relatives, deep diving often relies upon distant cousins. In that context, larger DNA segments can be an indication that the shared ancestor is more recent and may be easier to trace.
MyHeritage not only shows you all the matches you share with an individual but also how closely they match to each other. This is extremely helpful when trying to determine on which line you are matching to someone. If I can't find the common ancestor I share with one person, I might be able to find my link to his close relative. At the very least, I can determine which ancestral line they share with each other.
MyHeritage provides an integrated chromosome browser which is very easy to use. An icon on the Shared Match page tells you whether there is a triangulated segment shared by you, your primary match, and the shared match. You can compare your own DNA to the DNA of up to seven other people.
Under the "Advanced options" menu, you can download your shared DNA segments to an Excel spreadsheet and paste them into DNA Painter. This process takes less than a minute. When I'm ready to research my Mennonite Mohlers, I'll know exactly which portions of my genome came from them.