I think that the most striking similarity between both of them is that for the majority of the play, both Reverends are part of the "machine" in Salem that keeps churning out people accused of being "witches." Both men take a certain amount of pride in being Reverends and as men of the cloth, they exert a certain degree of power over others. I think that the primary differences between them is that Hale possesses a sincere belief to rid Salem of witches and the presence of the devil. While Parris does not say he lacks this, it is evident that Parris is only latching on to the campaign and emotional contagion in the attempt to secure his own hold on power. Hale legitimately wishes to rid Salem of witches, while Parris is more concerned with his image and how to bolster it. Additionally, I think that Hale is not afraid to take a stand, even if that means his expulsion from the proceedings. Parris lacks this moral conscience. Hale is shown to be quite learned, as seen in the opening scene when books are a prelude to his presence. Parris is not shown in this light, as he seeks to do display only what will enable him greater political and social power in Salem.
One way in which the Reverends Parris and Hale are similar is that, however ill-intentioned the one and well-intentioned the other, they both fail the people of Salem. Reverend Parris is more worried about his own reputation than he is about his daughter's health or the well-being of his congregation; he jumps on the witchcraft bandwagon because, if he gets ahead of it, it cannot run over him (so to speak). He isn't interested in truth. He's interested in power.
Reverend Hale is interested in the truth, but his unwillingness to stand up for people and risk pitting himself against the court rules until Act 3, when it is too little, too late. He seems a bit misguided, so sure of himself, his books, and his experience, that he cannot see that others might have ulterior motives. Then, in the end, he counsels people to give up their integrity in order to save their lives, though none of them do.
One minister lies and the other advises others to lie; though Parris is far worse than Hale, the result of their failures is the same: the deaths of innocent people.