when choosing which move to tech chase with (grab vs. usmash vs. nair) you need to visualize what is likely going to happen if they have optimal/pro DI. for instance, if you tech chase with a grab, and they're right below a platform at mid-percent where uthrow bair won't combo, it might be better to just tech chase with usmash because it will have a guaranteed follow up.
edit: in the situation i'm trying to describe, imagine doing a tech chase grab into uthrow on the platform, and then platform tech chase with bair. imagine where they end up (at mid percent, they wont get sent that far, can easily sweetspot ledge with a doublejump.) but if you did usmash -> bair/nair, they would probably be sent a lot farther/be forced to recover