I've owned both modules from near enough release date.
Since owning the Mi-8, I rarely choose to fly the Ka-50. Hard to say why, but I get more a sense of satisfaction with the Hip. I like the big weighty feel of it. If you want to blow things up with efficiency and precision, and less effort actually flying, you need the Ka-50. With the Ka-50s autopilot system, you can fly it with just a dual analogue gamepad; it's that good. With the Mi-8, I found I needed rudder pedals. Also worth mentioning, navigation is much easier with the Ka-50 and it's ABRIS moving map system.