It is is important to buy apples that are organic, unbruised & firm-skinned (as well as to avoid ones that were picked before they were ripe, which means they haven't developed as much nutritional value).
The one and only issue with apples from my point of view has always been that they've never really filled me up when I've eaten them as a snack (despite all the water and fiber they have in them). A friend of mine suggested that I try cooking them in the microwave, which sounded intriguing. So, I sliced up an apple into many thin slices, put them into a bowl, sprinkled some cinnamon over them, and then put the mixture in the microwave for 45 seconds. After it came out I added a dollop of low calorie whipped topping (sometimes I cook it with the whipped topping as well depending on my mood).
What resulted from cooking the apple with cinnamon was a dessert/snack that tastes just like apple pie. I'm not kidding! It is delicious (way more than I expected) as well as super filling, so I've started eating it for dessert instead of low calorie ice cream. I've played around with adding sugar, brown sugar, and some low calorie butter, although I like it best just with the apple, cinnamon, and whipped cream.