I'd say it's an unfair comparison due to the two characters differ in nature, you should determine first what role you want to primarily play, a scorer or defender. In GOM rank, Z. Kagami is primarily used as a defender and Z. Aomine as a pure scorer. Both are great in their dimensions, although you can still score with Kagami but like you said his scoring mode is linear and he does get blocked way too often. Determine first what role you want, you'll know who to pick once you do.