I don't do hdr all that often, normally prefer to make all my adjustments in Lightroom and photoshop. I have always preferred to shoot on AV but when a shot really screams for hdr I switch to shutter priority so the depth of field remains constant. If you use AV and pop off seven bracketed shots you'll have a huge difference in dof when you come to merge them.
Of course, if it's a windy day and you've got trees or whatever in the shot, then 1 stop shutter intervals will give you huge differences in movement... it's horses for courses.
I Pretty much always shoot with one stop intervals, the shot itself dictates whether I do 5 or 7 exposures.
