The question was who has made the most strictly from fight purses. The answer to that is definitely Tyson.
A quick google search reveals that De La Hoya's total purse earnings are more than $200 million, while Tyson is believed to have made somewhere between $300-400 million. So Tyson clearly earned more. This isn't surprising, since Tyson was making $25-30 million dollars not just in his big fights, but also against the B-level guys he fought right out of prison. De La Hoya has only pulled in that type of money in his big fights.
Tyson deserved to make the most, since virtually all of the highest grossing PPV's in history are his fights.

Now if you were to account for all boxing related income, then DLH would almost certainly be #1, since I'm sure he making tons of money with his promotional company. Tyson obviously never started a promotional company, although the thought of him managing and promoting other fighters is pretty funny.

But just fight purses, it's Tyson who has made the most.