I've played him top and bot semi often.
He can pretty safely farm and kite against juggernauts in top lane, which is nice. However, his immobility can make top lane a scary spot if the enemy jungler ganks a lot.
He can also clear the jungle pretty well, though his ganks are weak early and he is immobile. With Flash + Ult, jg Malzahar can very easily secure a kill for his teammate.
You have to keep in mind that Malzahar is pretty flexible when it comes to builds and can go AP, AD, or hybrid. He can also benefit from building somewhat tanky/bruiser since his ult locks himself down in fights and he is immobile making him vulnerable when squishy. You just need to experiment a bit more if you think APC mid is the only way to play Malzahar.