What do you use your phone for?
I use the Classic and really, security is not the main reason I use BlackBerry still.
It's got the best keyboard and way of navigating around. The iPhone is fun for like, videos and games and stuff. It's fine for texting and typing and phone calls. The Classic is reverse. It's fine for some games or videos. I'll sometimes watch a news clip or a YouTube clip on my Classic. It's fine. Good even. The speaker is good. But what I LOVE it for is the typing. I can pick it up, swipe up to unlock, then dive right into typing or going on the web browser.
Keyboard shortcuts become part of your life. Pressing N brings up BBM, or B for browser. You can do a lot of stuff more quickly on a Classic.
But be aware... if you're into posting on Instagram a lot, or SnapChat, you might want to hold onto your iphone and use it as an iPod touch. Instagram can be side loaded, and I had it, but it's better on my iPad. Never tried SnapChat because I don't have one. If your life is run by apps, I would rethink getting a Classic, but if you are adding a Classic in addition to your iPhone or keeping the iPhone to use on WiFi, then the Classic really can't be beat in terms of texting/email/ phone calls and web browsing.