I prefer the standing with a barbell, another chance to load the spine which is beneficial also REAL world as opposed to the leg press machine.
Vary the stance, also do them unilaterally.
I dont think it would be harmful but not sure holding in that position is that helpfull.
It is good to pause on the negative portion of the calf raise. the calfs have a VERY strong strecth reflex and a 3-5 second pause will aloow that to dissapate then you will have to use REAL muscle tension to preform the movement.
Vary loadas and reps but I would lean toward more heavy low rep high set. Just think they get loaded all day every day with VERY hig volume and minimum resistance.
NP hope it helps.