I use Shooter and Bullet Flight L2 by KAC. Both of those are geared more towards LR shooting/ballistics than what you're wanting to do though.

As for using the apps vs. dope charts, they do pretty much the same thing. I think the main advantage is that you're able to change different factors under different conditions and still be pretty close to your mark. Obviously, windage is going to be on the shooter, and the guys shooting tactical comps are more than likely using hold-offs as they're much faster... I don't think first round hit probability would change much if at all using an app vs. not using one though.