The shell I have been using for the past 4 years is Remington "Heavy Dove Load" 7 1 1/8oz. They really are the best and at only $3.39 a box you can't beat it (Academy Sports). Last year I shot 20 of these shells in 30 minutes and had my 15 birds. My personal best!!
This is a link to the dove hunts I've done in the past.
http://www.ryanaller.com/blog/?cat=4