Been to both. Assembly Hall is a terrible place to watch basketball. Balcony seats are awful and crowd noise has never been impressive when I've been there.
I'm a Purdue fan so don't take my word on Mackey Arena. (Don't take an IU fan's word either).
Do a Twitter search on it and see what others have to say.
https://twitter.com/FlemmingDave/status/953413920869494784
https://twitter.com/GreggDoyelStar/status/935708770956652544
https://twitter.com/jdemling/status/935714678080237569
https://twitter.com/TheAndyKatz/status/935675002741055489
https://twitter.com/Graham_Couch/status/833057603542462464
Plenty more out there.