I LOVE the heavy barrel of the OMS, and prefer it over the OMM in spite of the inferior sights. The OMS had a much shorter production run, so I consider it more "collectable." On the other hand, a Pre-1961 OMM has those gorgeous full-checkered stocks .... No, the heavy barrel still carries the day with me.
I have examples of each, and prefer the OMS. I don't find any fault with the Coltmaster rear sight. It's the small Coltwood stocks that I don't care for. I've changed them out for later OMM type target stocks. Not only do they fit my hand better, but they balance the look of the gun with the heavy barrel.