Do You prefer arched or flat MSH ?

For bullseye style shooting do most favor flat or arched MSH ?

Arched feels the most comfortable but I shoot a flat MSH better.
- Dave

Always flat with a beavertail grip safety for me. With a GI grip safety I could go either flat or arched. The service pistol I've been borrowing has a GI grip safety and arched MSH and I shoot it well.

Flat.

I like an arched mainspring housing.

Flat always feels better to me. In fact decades ago when I had a 52 I altered the backstrap to get rid of the arched shape at the bottom. In spite of that, I earned all of my leg points with an arched housing and GI grip safety.

Flat

I think that it is something that each shooter must figure out for him/ herself.

I agree with BE Mike...
An arched mainspring housing, along with a medium length trigger, is the right length for me to pull the trigger straight back.  The gun also seems to line my eye up with the dot using an arched housing.
As a side benefit I find it easier to position the gun correctly in my hand due to arched housing sticking out.