If you've been disappointed with CX in the past then I would be surprised if MU improves on that. CX, by and large, has better equipped planes, better trained staff and better service than MU (and CZ). If you do fly MU/CZ in the future then you'll discover that yourself. There's no doubt they're trying to improve and I think we will see that in the coming years but it will take them a long time to reach CX levels.

As you mention MH has plans to join OW in the near future and I would suggest sucking up CX and/or other OW when you fly to Europe for the time being until MH joins. This makes even more sense if you already have miles and/or status invested in a OW mileage program.
I'd suggest the same when flying between Malaysia and mainland China, although I imagine you'd have to route through HKG every time when flying a OW carrier (CX/KA).