It would be mango if it was as little work as an apple. But an apple is so versatile. Some might argue watermelon, or even banana. Watermelon you need a knife (unless you want to eat like a barbarian) and a banana can’t be thrown in anywhere in your bag. Bananas get squished. Apples might get a dent, but it holds up. And a kiwi has the same problem as a banana. Easily bruised. Plus, how are you eating a couple kiwis on the go? Not like an apple you aren’t.