Conclusion
In the end, the decision is based on what matters the most to you. If you're stuck using an ancient iPhone such as the iPhone 4, then upgrading now probably isn't a bad idea. The iPhone 5s will still be a great phone after Apple's next smartphone launches, and it's more than capable of handling your everyday needs. But if you're using a newer iPhone, such as the iPhone 5 or 5c, and are looking for something a bit bigger without switching to Android, it's probably worth the wait.