They are very different - DeNiro centers his film, Pacino's great trick - and it is a great trick in Paterno - is to be the void at the center of his film - it was an amazing display turning off his charisma and presence to be that sad guy.
I like Pacino a bit more because I like his film a bit more......and because he didn't have anybody to play off for the first time on HBO - no Streep, Sarandon or Mirren. DeNiro had to do more heavy lifting in his characterization, Pacino had to find the right note and maintain it/manipulate it.
I think they are both rather great in their own way......
Pacino. I don't think he was given enough to really do, but he was convincing as Paterno. De Niro struggled to keep his performance from being leaden; what moments of strength there were ended up mired in a general air of mediocrity.