Beware, the original 44 (M39, 8 or 13 blades), unless adjusted by the vendor, DOES NOT reach infinity.
It's amazing to see that many people don't even notice that!
Same thing applies to the Helios 40 (original "silver" version, M39). Bought mine cleaned and refurbished, with the M39>M42 ring, and the seller had already taken care of the problem. If you find one on the cheap it would probably miss the infinity by a little bit.
The solution is to unscrew (that simple!) the lens head from the barrel, take out the washer that you can find underneath, and sand it with sandpaper until the thickness is reduced enough to allow for infinity focusing. It should be a third of a mm, or something like that.
When I did it, it was spot on after the first tentative.
Pay attention to change the position of the ring and sand in circles, to keep the washer as flat as possible.
Now my Helios 44 silver (8 blades) is one of my most favourite lenses.
All the 44's are "sharp enough" stopped down at mid apertures. The newer the sharper, of course, but I believe that what changes the most across versions is the bokeh.
IMHO the 44-2 is the best balance between the two extremes, and of course the 44-K is the most usable cause it can be quickly swapped with any other PK mount
Even the 44M is perfectly capable of smooth portraits wide open. I do plenty of portraits, but I can't post for privacy reasons. So here is one of myself:
Selfie, a few years ago