I have the Opticon MM4/60. I mostly use it with the out-of-production 32x wide eyepiece. I also the the SDLv2 for more reach or if I want the zoom. It is very light and compact, which were two of my big check boxes, along with a reasonable price. I'm happy with it. I mostly do photography, so the scope is secondary for me.
I use the angled MM4. It can rotate around the tripod mount, so in a car I can turn it sideways and it mostly works fine, though I do not use it this way much.
I have not used the Kowa 602. I think the MM4 is a tiny bit more compact based on the specs. They are about the same weight.
Based on someone else who recently went through the purchase and comparison process, he much preferred the TSN-660 to the MM4 in terms of the view and other features. He ended up getting the TSN-663. Again, I've not used that.
Marc