I moved from the droid to the iPhone 4, 32 gb on launch day.... never looked back.
iPhone 4 has better (faster) camera. droid took literally 5 seconds to autofocus/flash/take picture.
Droid would spontaneously delete whole text message threads even if they were locked (one of my biggest irritations with the droid... but its more of a software problem than actually phone/hardware).
This isn't really a problem pertaining to the droid but more of the Android OS, but it simply is not as developed. Games do not render as smoothly, apps crash often, there's not as big of a selection etc.
You definitely can tell the difference in quality between iOS and android.
Android is more for customization, which was sorta cool to experiment with until your phone crash and would never get out of the reboot screen.
iPhone is more is for simplicity and stability- which I would choose, hands down, over Android and fragmentation.
Those are the biggest things I can think of... if there's anything specific you want me to compare let me know, otherwise, good luck in making your decision!