Untreated will not last. Treated will potentially release chemicals into your soil/food, though you can line the interior of your bed with gardening plastic.

There are also slightly more expensive options for treated wood (branded EcoWood and so on) that are a good option.

(I have seven 1.2x2.4m raised beds in my garden. Bring in fresh soil otherwise you will get endless cycles of weeds - that's still one of my main problems two years in.)