As many of you know, each year the Environmental Working Group (EWG) releases 2 lists: The Dirty Dozen, and The Clean Fifteen.
The Dirty Dozen lists the top 12 produce items that carry the MOST pesticides. The Clean Fifteen lists the 15 produce items that carry the LOWEST number of pesticides. When I'm shopping, I reference both of these lists regularly to make decisions about what to buy organic, and what doesn't need to be (based on budget and availability). This year, strawberries, spinach, and kale top the "dirty" list.
That said, if you're making a choice between conventional produce or NO produce--go conventional. Generally speaking, the value of the fruit or vegetable outweighs the toxic load it carries.
Do note, the higher up the food chain you go, the more important it is to eat organic. For animal proteins and products, choose PASTURE RAISED whenever possible. For fish and seafood, choose WILD CAUGHT. The healthier the animal, the healthier the meat, eggs, dairy, etc.
Check out the new EWG lists here: