Had several MC and SC 50/1.8 Zuikos. Latest 50/1.8 had plastic aperture ring which felt like a downgrade to me. Couldn't notice any difference between SC and MC 1.8s performance-wise so I settled for MC version with metal focusing ring.
Also had several 50/1.4 Zuikos, two of them with serial above 1000000. Single coated 50/1.4s performed noticeably weaker compared to multi-coated 1.4s. But a multicoated lens with 700000+ serial was already retty good.
Finally, I had 50/3.5 macro too. It delivered the quality you would expect from a macro. Plus it was excellent at infinity too. No worse than 50/1.8 and 50/1.4 at f/4 and smaller. But I couldn't omit those entirely because of the long focus throw of 50/3.5.
In the end, 50/1.8 was the last 50 mm Zuiko I kept, until I went for a 35mm prime. Why not 50/1.4? Because 50/1.8 balances better on dinky OM cameras. Also because the difference between performances of 1.4 and 1.8 was negligible for my puny 8x10 prints and scans made with non-drum lab scanner. Another sentiment you will often hear is that 1.4 gives a brighter viewfinder. However, with big and bright viewfinders of OM cameras, I couldn't notice a drastic difference.
Other users will give more comprehensive opinion, my OM hobby only lasted for 5 years or so.