My ex grew up on a dairy farm - they would get the water boiling, walk out into the field, grab some corn and throw it into the pot for 90 seconds and chow down. They would laugh at the tourists who would pull over to the side of the road to grab a couple fresh ears of corn from the field and take off - they planted field corn (cattle feed) along the road. She earned her college money as a corn taster for Jolly Green which is why she will never eat canned corn.
Okay, in the store pick up each ear of corn - if it does not feel heavy, put it down. You want corn (actually any fruit or vegetable) to feel heavy for its size. I do not know how or why we know this but when we (you and I) pick up and kind of shake something, it feels heavy for its size or it doesn't - what we are learning from this is whether or not it is fresh. Fresh fruit and vegies still have their natural water weight and feel heavy; with corn, as the water aspirates sugars are changed to starches. Never buy more that you will eat that day - tomorrow, the corn will not be as sweet. At home, once you get the water boiling, set a timer for 90 seconds and drop the corn into the water. DING! pour it all out into a colander in the sink; coat a slice of bread with a thick layer of butter and roll the corn on it voilà your corn is buttered (or get a stick of butter out of the fridge and use that to coat the corn) and chow down.
Today I bought one yellow and one bicolored ear - the bi-colored one seemed sweeter; I will make another test tomorrow from a different store. Well, heck I think I am going to make this test until the season is over.