Even while I am reluctant to compare them, or favor one over the other, I have to go with Doubt on this, and am somewhat surprised to see it dismissed in such a matter-of-fact fashion on this thread.
I enjoyed August for the fun house ride that it is, and found it well acted, directed and designed, tho I think everyone in the press and on the chat boards sure gives that first act a free ride. There are some truly indelible scenes and moments. But in retrospect, some of the twists and turns felt gratuitous, even calculated and manipulative, and some elements of the play even boarder on the hokey. I also felt that the poetry and searing writing that enriches great American dramas of dysfunctional families like Long Day's Journey and Death of a Salesman (plays that August has been compared to) is just absent here. I started to wonder why I was spending so much time with the Weston family, even while I enjoyed myself. I admired the play's balance - particularly the way the curtain lines for Violet in Act One and Act Three refer to each other, but the way an author's voice can reach out and directly speak to you just never happened for me at August.
Doubt, by comparison, I felt packed a lot into 90 minutes. It was lean and compact, without a wasted word or moment. It also worked on two levels for me: first, as the theatrical melodrama it is on the surface. It's a great vehicle for all four actors. But the phrase, "A Parable" is an important one, and I think what Shanley is saying about the state of moral certainty in this country at this time of our lives is and continues to be incisive. In politics, the press continues to flagellate any candidate or representative who dares to "flip flop" on an issue. To question, or to express concern or reservations is seen in this country as a sign of weakness, instead of the hallmark of a free thinker. For me, that was what Shanley was writing about, more than the case of whether Father Flynn was actually guilty or not. As the Iraq War continues to rage on, and our leaders in hindsight try to distance themselves from the collected intelligence that got us into it, I think the issue of expressing doubt, raised by Shanley's play, remains even more vital and pertinent, rather than just fodder for a hit show that captivated Broadway and the regionals for a season or two, as suggested above.
Begin at the beginning and go on till you come to the end: then stop.