Ok, this is a can of worms.
Unicomp makes Model Ms with the original machine parts bought from lexmark. Plastic is a little thinner and they're not has hard core heavy but it's buckling spring and a nice way to have a new M with USB, windows keys, etc.
I personally am a huge fan of Topre switches and use one as a daily driver. But they're a hybrid switch and much quieter than the buckling spring.
I am not a fan of most cherry switches. Either they're too loud, too mushy, to quiet, too shallow, too deep, to stiff or the feedback is all wrong. The only keyboards that satisfy me are Topre, buckling spring and Thinkpad keyboards.
Others might have a preference for some cherry switches. I don't know. I've tried them all and none touched on all the bases I need.