Is there a rule of thumb as to whether it's better to pick up Metro North at Grand Central or Harlem-125th?

I've mapped out the route on google and it seems like any difference is within single digit minutes (assuming you take express up to Harlem-125th). I'm not familiar with either MNR terminal, but I assume Harlem-125th would be smaller and quicker and easier to navigate.

What's your preference? Assuming you're already in the subway system so taking the subway up to 125th wouldn't cost anything extra.

Thanks