What's often overlooked is that there is in fact a nice compromise between the two. You could use a long numeric passcode, and it'll give you a keypad just like when you use a 4-digit passcode, as you can see here. You do need to press a button after entering the digits, but that's because it won't let someone guess how long it is.
I think this is even more useful when coupled with the Touch ID in iPhone 5S. You can still use the fingerprint to conveniently unlock most of the time, and you'll feel more safe in that there is less of a chance someone else could bypass that and unlock using a passcode instead. And the "autofill" of the passcode when you press your finger to unlock doesn't reflect how long the passcode is, either. It just shows nine dots all the time. A perpetrator won't be able to guess the length of the passcode by glancing at your screen.