As good as it can be

The problem with the stitching is not the app; its the fact that you can only get a truly perfect panorama if your camera is mounted on a special device that keeps the lens exactly centered on its focal plane as you turn it around. To do this even on one axis (for horizontal panoramas) is tricky enough, but its much more difficult to do a full spherical panorama. If you think youre ever going to get good spherical panos by casually waving your phone around, you are always going to be disappointed. It is quite literally not possible to solve this with software alone.

Stormchild about 360 Panorama, v4.4.2