I think Harvard is a much better biostats program than Berkeley biostats. I think Berkeley stats is a better program than Harvard stats. If you are dead set on biostats go to Harvard. However getting a degree in stats gives you more flexibility. Depending on what you want to do, going to Berkeley gives you more options for the future.
I'm just another stats/biostats PhD applicant this year. I've been working at Harvard biostats for a while. IMO this is a more applied department, since as you know they have arguably the best medical school in the world therefore many high-quality data. But they do have some theoretical people, like Rajarshi Mukherjee, Tianxi Cai, Junwei Lu, etc.
Another factor you should consider is what topics in biostats you're interested in. For example, if you're interested in statistical genetics I'd vote for Harvard biostats, for example Xihong Lin is a pretty strong faculty in this area. If you're interested in causal inference, Harvard is good at it too but I personally favor Mark at Berkeley. Overall I agree there are more people working on theory and methodology at Berkeley stats than Harvard biostats. You can't go wrong either way, best of luck to your decision!
