A while ago I was medium-slow and smooth, and it worked pretty nicely, although I couldn't really turn any faster. Then I got a little faster at turning, and a little less good at lookahead (from lack of practice)... so now I'm medium-fast and usually-smooth. I could probably save like a second from my average if I learned to be smooth again, but I kinda don't care enough.
But yeah, if you gotta choose one, I recommend slow and smooth (with practicing TPS on the side). Once you have that down you can slowly improve your turnspeed until you can turn at your near-max tps with no pauses. (And then I guess you just practice turnspeed a lot, because that's the only way up from there.)