The considerations that make me choose a particular size don't tend to change much with tech.
Size 1 for AMMs and saturation attacks.
Size 7 for something just large enough for a sensor or a 2-stage approach, a small footpring and 1HTK in a box launcher.
I may have one larger size which be pretty much anything, size 25 seems a good compromise - large enough for most complicated things I may want to try, not excessive for single-stage use.
While I may design multiple versions (different sensors, different ranges for fighters and warships etc, different splits of warhead and agility), standardising on size seems good.
Also, I don't generally upgrade things very much... old ammo will be expended liberally, obsolescent ships will be used on the fringes in peacetime and be used for risky missions in war.