Quick and simple test of three 55mm standard primes shot wide open at f/1.8 on a Panasonic GH2. All shots were made using the Standard profile at 0,0,0,0 using the Cluster X Drewnet v.8 firmware hack.
Surprisingly the Mamiya/Sekor seems to be the sharpest. The Takumar tends to "glow" a bit more in bright light and has a "warmer" look but that could be from a bit of yellowing. The Fujinon is an older non-EBC, but the results look good, similar to the Takumar.
Unfortunately the Mamiya/Sekor and Fujinon use a special locking pin system that keeps them in 'auto' mode. So to close the aperture they need a special adapter or need to be modified (which I will not do since I use them for analog photography).
Update: I bought another M42 to Micro 4/3 adapter on ebay that has a small 'rim' or 'edge' just under the screw mount threads which depresses the 'auto' aperture pin. So now I can use the manual aperture settings on Mamiya/Sekor and Fujinon lenses.