I've tried a few Linux distributions in the last few days, I suggest you try LinuxMint - it seems to be the less painful option. I'm not sure what desktop manager they use, but it's definitely better than stock KDE or stock GNOME.

For KDE, the best experience at the moment seems to be Neon, although I've not tried OpenSUSE.

Openbox + compton gets me the same smoothness as Aqua, and is much more configurable. You can make it look and feel 99% like Aqua, or you can go another direction and make it exactly what works for you instead of cloning another interface.

Can't disagree with that. The way it functions and the plethora of apps you get with it are good enough for me