If I thought there was ONE best tuner I would tell you. It is not as simple as that.
Speaking only from the bleachers here. But, amen. Tuning, avocationally with one's own bike or professionally over and over is as much art as science. When John Golden was still active locally I used the Power Commander. Not because it offered the most tuning options or could control the greatest number of engine management parameters. In fact it couldn't. But John was an artist. Both an excellent and a diligent tuner that did a wonderful job; over and over again. That's why it has been repeated whenever someone asks "uh, what should I use?" that the answer should be the choice of whatever good tuner the bike owner is going to have do the work.
Lacking a gifted and/or even diligent local tuner any longer I was pleased to see the EMS kit become available. Readily admit that a brilliant tune would almost certainly do a bit more. I might or might not notice the difference. But this device gets it as good (or likely much better) than I ever would chasing cells with a computer in the saddlebag working from someone's base map that was never base to my bike to begin with. It's not that I'm incompetent. I'd get it good. But I readily admit never get it great. EMS has, on my bike anyway, got it pretty close to great.
A gifted tuner with a few hours time would, I'm confident, find improvements to be made; subtle but not gross. Improvements that might or might not be worth the expense of time and hard dyno time on the bike (not to me, your sentiments may vary; whomever you are). Lacking a truly talented local tuner who would also be a tune and forget it option (because you just know he's going to have it right) I'm very pleased the EMS package is out there. It does a great job (at least on those I've worked with) and I don't have to spend hours dialing it close (because I can never truly know if I've got it dailed "in" anyway).
If I had an absolute known to be iron clad artist of a tuner as an option again this would still be an open question. Most of us don't though. Most of use "ok" or "decent" spinning the wheels on their local dynos. Most of us don't have GMR close at hand. Lacking those options a bolt on and forget it option that is very very good is hard to turn down when the alternative is going far and wide chasing an ephemeral difference we may never feel in the seat of our pants anyway.