As a recent switcher who tried both, I'm now a Colemak Believer.
My story:
(TLDR: Made a serious effort to learn Dvorak, but eventually found that Colemak works much better for me.)
I never learned to properly touch-type. I decided I wanted to learn - properly - by starting over with Dvorak. (At the time I was aware of Colemak, but rejected it as just a "tweaked qwerty.")
Dvorak made a lot of sense - AT FIRST. But after a month, I started noticing the problems. The nonsensical placement of I vs U, the hard-to-reach F, the scrunchy L. These are not serious issues when you're punching keys with your whole hand in a left-right-left-right pattern on a mechanical typewriter, but they tangle and stress your fingers on a modern keyboard.
I spent some time trying to "fix" Dvorak with custom layouts, and tried Workman for a week as well, before looking again at Colemak.
After a few days with Colemak it clicked, and I've been using it for almost 3 months now - first at home, and now at work as well. I even program using it. My speed is about to surpass my former qwerty speed and I'm still improving steadily.
(And while it was not originally important to me, the fact that ZXCV shortcuts stay the same as qwerty is VERY nice!)
The relative "popularity" of Dvorak is not really a selling point. Once you're relegated to the minority of alternate-layout users, it hardly matters which alternate you use.
In conclusion:
Dvorak was designed for a mechanical typewriter, with emphasis on hand-alteration. Colemak is designed for a computer keyboard, with emphasis on avoiding same-finger strikes. If you're starting fresh, the learning curve is the same for both; if you already touch-type qwerty then Colemak will probably be easier to learn.
So in my personal experience, Colemak is far more usable than Dvorak, and I'm glad I made the switch.