Honestly, if an outdoor bench is going to sit in full sun all day, my top recommendation is teak. It has natural oils and rubber that act like a built-in sunscreen, so it resists UV damage, cracking, and warping much better than softer woods. It also stays cooler to sit on than metal or composite. The main downside is the price.
If you want the toughest possible option, look at ipe, also called Brazilian walnut. It is incredibly dense, naturally resistant to sun, rot, and insects, and can easily last 25 to 40 years outdoors. It weathers to a silver-gray if left untreated, but if you want to keep the rich brown color, apply a penetrating UV-protective oil once or twice a year. It is heavy and hard to cut, so pre-drilling is a must if you are building the bench yourself.
For a more budget-friendly bench, cedar is a solid choice. It is lightweight, stable, and rot-resistant, but direct sun will bleach it and cause surface checking unless you keep it sealed with a UV-blocking stain or oil. White oak is another good mid-range option: it is strong, weathers well, and looks beautiful, but it still needs periodic oiling to avoid drying out.
Avoid cheap pine, fir, or spruce unless they are properly kiln-dried and pressure-treated, because constant sun and heat will cup, twist, and crack them quickly. Also skip thick film finishes like polyurethane on outdoor benches; they peel under UV exposure. A penetrating oil with UV inhibitors is always better.
Whatever you choose, use stainless steel hardware, allow air to circulate around the bench, and clean it once or twice a year. That will keep a direct-sunlight bench looking good and structurally sound for decades.