I own a bunch of these apps. The only ones I use anymore is Strelok Pro and Applied Ballistics. Strelok is great because it's very user friendly. Input is very simple and fast. I love the ability to see the ballistics solution with your particular reticle.
Applied Ballistics is what I use when I'm shooting over 1000 yards and can take my time. Not as quick, but I think the ballistics curves are just a tad better over 1000 yards