Indeed, when entering combined inputs one by one starting with my off-hand my accuracy was higher and I found myself using that technique occasionally during practice, especially when I had made a mistake and needed to repeat an input. However, as my speed increased, eventually I tended to move the sticks simultaneously.
I wonder if it was easier in practice to move both sticks simultaneously, or one after the other and then release them simultaneously. Because the currently most commonly accepted psychological model two-handedness[0] would suggest the latter, and that you start with your off-hand and finish with your main hand.
[0] http://cogprints.org/625/ Asymmetric Division of Labor in Human Skilled Bimanual Action: The Kinematic Chain as a Model