German Shepherd dog

8:10

8.5:10

9:10

and which could be techniqually better or correct gait ?

Keep in mind gait is also effected by many other things also, front and rear angulations, lengths of upper arm and croup, strength of pastern, tightness of feet, conditioning, placement of stifle...the dog itself is a machine of movement.  A dog can correct HL proportion and still be a mess based on other faults.

9:10 to me is too square, I would imagine the dog would have limited rear propulsion.  By the same token, a lengthy dog to me often has a weak back and this is transmitted in movement also.

These are only my observations in my very limited experience, I have only been in the breed about 10 years...someone correct me if I am wrong.