If i'm going by your Thread Title - I most prefer DirectAdmin as a control panel.
If I go by your poll and question in the thread, i'd say most hosts prefer Cpanel - not because they've tried em all, but because Cpanel was the first one they've used. Why change what you already know well?
Control panels are such a personal thing. It's a like the make of a car. I don't like Fords for a couple reasons, which are really inconsequential to the actual functioning of the car. The car still runs, I could drive it if I had to. Control panels are the same way - they function just fine, but what is your preference.
I'd say Cpanel is the most popular simply because more dedicated hosting providers offer it included with their service = better exposure. That coupled with the fact people usually stick to the first control panel they use....and there you have it.