Left-hand low since 2009 aside from a very brief period where I experimented with a sidesaddle putter. I like a straight-back-straight-through motion but I'm not too technical about it. I'm much more exacting about alignment, posture, and rhythm - left eye right over the ball, toe line pointed dead-parallel to target line, putter swings like a metronome at the same tempo as "Live Forever" regardless of length of putt. I sometimes catch myself audibly clicking out the drum intro between my teeth as I stand over the ball.
I've gone to one of the Superstroke grips and don't envision going back to something smaller. I've used an $80 Cleveland mallet-blade for almost 10 years. It has more than paid for itself, and putting is easily the strongest part of my game day in and day out.
At least on reasonably fast greens...
I played a couple tournaments on slow greens this year, and my putting advantage disappeared in both of them. I will often go right-hand-low and hit sort of a "chip-putt" when I putt from well off the green, and I thought of going to that shot on putts over 20 feet or so on those slow greens. I think it's a lot easier to control speed when you need to put a "hit" on the ball when the dominant hand is low, and I suspect that might be why left-hand-low didn't really become a thing until green speeds consistently started running above 10.