Of the three, Theodore Roosevelt was perhaps the greatest reformer. He considered himself a progressive, even though he was a Republican and was largely responsible for breaking up the gigantic business trusts which had dominated the American economy. Since Congress was reluctant to enact legislation to regulate trusts, Roosevelt ordered his Attorney General to bring suit against them. The two most important cases were the Northern Securities Company Case and the Swift and Company Case which broke up the Insurance and Meat Trusts.
Aside from that, Roosevelt was largely responsible for the Pure Food and Drug Act, and the Meat Inspection Act, this after he read The Jungle by Upton Sinclair. He couldn't believe that the conditions described by Sinclair were true; and when inspectors assured him that they were, he acted immediately. He was also a major element in the establishment of National Parks. Notably, Roosevelt was the first President to invite a Black person to dinner to the White House as an invited guest, namely Booker T. Washington.
Taft was hardly a reformer. He was more of a caretaker President, and quite conservative. He supported a lower tariff, which Roosevelt had opposed, and so offended Roosevelt that the latter ran against him for President in the 1916 election. His third party effort was just enough to give the election to Woodrow Wilson.
Although a Democrat, Wilson turned a deaf ear to social issues. He said that child labor was a state issue, so the Federal government should not be involved. He did not support Women's suffrage, and in fact was called "Kaiser Wilson" by some women's rights groups. He also was quite racist, and did nothing for the cause of Blacks. In fact, he fired all Blacks who held government positions when he took office.