Looks are entirely subjective, but we prefer the Michelin. It has a nicer tread pattern and more profiled sidewall angle as it sits on the rim. The Continental sidewall is a thing of beauty though.
The Conti is slightly lighter to steer, perhaps a little more dead in the center of the steering but turns slightly quicker. You get more feel and feedback through the Michelin, but the Conti is more comfortable as a result.
Traction and Braking
The Conti seems to have the advantage in both the dry and wet, in braking and traction. The braking is especially stunning in the dry. Traction you feel the diff having to do less work with the Conti, and the traction control is less invasive. The margin is larger in the wet where the Conti has the clear advantage.
Cornering Grip / Balance
Under cornering the advantage switches back to Michelin. Outright grip levels seem broadly similar, and the Michelin even has slightly more understeer than the Continental, but the extra steering feel the SuperSport provides gives you more predictability and confidence around, and past the limit, meaning you extract more from the tyre. The Continentals balance can switch between neutral and oversteer on the M3, and gives you less feedback which makes it slightly harder to control when flat out, but still an excellent tyre.
NVH (noise, vibration and harshness)
As mentioned earlier, the Contis have a slight comfort advantage, crashing less over road imperfections and pot holes. One interesting result was the internal noise test, both the Michelin and Continental measured near identical results, but the noise the Conti produces is a slightly lower frequency which makes it easier on the ear on most surfaces.
We were not able to make any objective wear data, but looking at tyre tests, user reviews and looking at how our tyres have been wearing, this is still one area the Michelin will have a noticeable advantage in.
This is an incredibly difficult conclusion, these are the two of the most focused performance road tyres on the market. From our testing, if you ignore wear, the Continental is objectively the better overall tyre, it is stronger under traction and braking, offers similar cornering grip and is more comfortable than the Michelin. The margin is incredibly slim, but real.
The interesting part of the conclusion is when we choose a tyre to leave on this car now the test is over... and the answer is the Michelin. It might not have quite the overall grip of the Continental, but on this car, in these sizes, for the driving requirements and style, the Michelin is better subjectively due to having the nicer steering feel and balance.
With the margins in outright objective performance so close between all the best maximum performance tyres on the market, it's often the subjective aspect of tyres which will make a bigger difference to your day to day driving.
Had the vehicle been an Audi RS6 with the priority more comfort and safety bias, the Continental would have likely won. But for this M3, the Michelin just about takes it.