I'm very sensitive to the distance from the back of the grip to the face of the trigger. Too long is utter disaster. I can't get a clean break in dry fire without serious amounts of contortion of my hand. When the distance is short, I can do just about any damn thing with my right hand and get beautiful breaks.

I like flat triggers and run them in my precision AR's for the reason Peter states above. If you're going to go that route, I'd strongly recommend a grip with replaceable back straps in various thicknesses. Magpul's version works well for me. Once you get it put together, you can fiddle with the various inserts and see what gives you the most forgiving hand position.