My wobble with the 44-2 comes from the fact that the base is so small that it rides on the actual m42-K adaptor and does not contact the camera mount at all. So on mine the "wobble" comes from how much play there is in the adaptor.
Does that make sense? Either way it is not an issue for how well the lens works.
Having said that, the 44-2 with the pre-set ap is a joy to use... If you are not used to preset ap rings, it takes a few minutes to get used to it, but when you do you dont want to go back....
NoMaD and JohnBee are right... the 44-2 is smoother and a little softer, the 44M6 is sharper and a little more wild in its bokeh in some conditions.
But they are fun and very good lenses... My most used lens this last year.
Helios 44-2 I believe my 44M is closer to the 44M-6