The Novak design is by far the best. I love what they've done with the replaceable stators and such. Now that all the aluminum parts are easily replaced, I'd like to see them offered in different flavors, like popular colors and maybe a smooth surface rather than the ribbed can. I also think Novak makes the best sensor harness, though I'd love to see them use all black wires and connectors, for those of us that can only get it done on the bench.
On the track (13.5), I find the top speed is about the same, but the DUO motors have a more linear feel to them. The Novak seems like it's got a LOT of rip down low, kinda soft in the middle, and then fast on top. I think it makes the Novak harder to drive consistently, though I could see it possibly being an advantage on a tight/technical track if you can control it. The DUO feels like it's got power all over, but not so much that it upsets the car.
I've tried most of the other brands, and don't really feel like they've got anything to offer that Trinity & Novak doesn't already do better. I'd love to see an LRP x12 in spec winds, though, 'cause their mod motors are wonderful.