There are a lot of arguments you can make as to which testing type is more important. If the app doesn’t function correctly that’s obviously a problem. But if it’s not intuitively usable (or just plan not usable), then it’s also useless in the eyes of users. If it can’t handle heavy load you’ll lose some users forever. If it leaks data you have upset users and the media to contend with, and your company’s reputation can’t handle that hit.
So which app testing type is the most important? You tell us. Vote in the poll and leave your opinion in the comments.