I've flown both in business class on medium haul flights within Asia. To me, the important fact is that both had 2-3-2 seating in business class, which I consider to be totally unacceptable. IMO OP should start byy examining aircraft types and business seating configurations.

MH allows you to order your main course in advance, although the system doesn't work flawlessly, in particular for direct flights. Still, it gives you more options than KE meals.

Both airlines seem to have an excess of young subservient FAs, although the uniforms are very different. Overall I didn't see big differences in service, F&B, seats (not true flat beds on my flights), lounges (taking the inferior satellite lounge at ICN into account and noting that you must find some one to request alcohol at the bar in the MH lounge at KUL), etc. although I'd probably give the combination of the KE lounge in the main terminal at ICN plus ICN airport itself a slight edge.

I would expect KE to be more expensive.

Another issue is which FF program you want to use.