I've had really good luck with the 420 first in the street MSM and then in the track beast. My tuner specializes in Hydra - mainly for Toyota MR2 builds but he helped Hydra develop the software so he knows it inside and out. I asked him if he would be willing to tune my Adaptronic/Wari and he said sure.
There was a learning curve involved. I was much more familiar with the software and he is a genius with fuel and ignition tables but in the end I got a great tune. The basic fuel and spark map in the load cells are the absolute easiest part of a tune. It doesn't matter what ECU you are using. If the tuner knows what he is doing, that part will be fine.
The magic is in the other 95% of the bullshit that comes with the tune. Are the sensors calibrated correctly? Does the car stumble at idle at certain ambient temperatures? How is the transient throttle? Do you see a voltage dip in certain circumstances that causes other system problems? The list is endless. This is where it really pays to have a tuner/installer that knows the product.
My guy would have taken a week to learn all that stuff for the Adaptronic and would have been fair charging me for it but my tune was on a dedicated track car so I only cared that it started, idled on grid and that the load cells were spot on. All the rest of the details I don't mind tinkering with myself as I go along.
The support for MS is great and it is clearly the favorite for many reasons. Like many things in the consumer world, ask yourself what you need and what you want and buy accordingly. I beta tested a new harness for Travis in '09 so I am pretty well invested with Adaptronic. It works fine for my needs and I understand the software/hardware. If I was starting from scratch would I have a different ECU in the car? Probably, but I'm not so I don't.