He's been the stingiest in terms of giving them out for people who deserve them on account of being ill-served by the criminal justice system, but he's been the most liberal in terms of bailing out his co-conspirators and politically connected elite.
Do we have a list of the “quality” of all presidential pardons?
It may be that proportionally some presidents show certain “favoritism” while others less. But given some pardon in the thousands it’s hard to say without further study that in absolute numbers one self serves more than another except by using biased heuristics.
Trump was never Assange's friend, and Assange was foolish to assume the enemy of his enemy would be his friend.
Given the way Trump operates in general, there's nothing in the long term that benefits him about having a whistleblower running around free, even if that whistleblower did significant political damage to his opponent one time.