I prefer internal so I can use any neutral clutch combo--if you are going to race you will play a lot with clutches---flywheel weight, multiple discs, etc, etc

I prefer external so the crank can more economical balanced for a customer and it won't take so much heavy metal

I prefer internal if the rods are a reasonable length(bottom of piston clears conterweigth)

I prefer external for some spec racers so that I can cut down the counterweights of there cranks for an ultra light rotating mass

and on and on and on