Mutombo has 1 more blocks leader title and a higher peak at 4.5 bpg compared to Zo’s 3.9.
However, Alonzo’s late age run really impressed me. Even after his kidney problems, during the 2005 playoffs, despite playing just 17 mpg, he managed 2.2 bpg. This included 3.0 bpg during the ECF. In the 2006 Finals, Alonzo also managed 1.5 bpg. 1.5 bpg isn’t a lot by an elite shot-blocker’s standards, but he was playing limited minutes, was 36 and literally hampered by a life-threatening health condition.
Personally have to go with Zo. I believe Zo was more athletic & had a slightly more expanded block zone on the court — contesting shots to nearly 8’ or 10’ from the basket. Mutumbo had more formidable size and equaled ferocity. Both of them being prized centers under Coach Thompson makes them more similar than different tho, and winners on & off the court.