i would take the kv2 any day since i never would pick an isu for its AT skils sinces it bounces to often for me. and AI wise the isu has way to much trubble hitting units on a hilly terrain then the kv2 bcs the kv2 shoots in a sort of curve and the isu in a Straight line which is terrible at hilly terrain. also kv2 has a huge range while immobile and also this range increases with vet2. so if you liked building howies but find it not possible to buildthem anymore bcs of stuka dive bomb, then get a kv2 since it is a sort of mobile howitser (it uses the same gun lol) it only has not as much range as howi but its mobile so you can move it up.
KV 2 pen: 1
60-200 200-160.
ISU152 pen: 260-200.
lel 1
KV range when siege: 70
ISU152 range on move: 70
lel 2
ISU has problem when terrain is going up and down.
KV2 has huge problems when it's stading on a lower/higher terrain when gun is aiming up (never gonna hit anything)
lel 3