Trial and error and word of mouth are the best sources of information fro choosing a sunscreen. For true broad-spectrum (UVA and UVB) protection the active ingredient list should include Parsol 1789 (avobenzone), titanium dioxide, or zinc oxide. Without at least one of these you are sacrificing UVA protection. Studies have shown that sunscreens with substantial UVA protection can prevent sagging and wrinkling of the skin due to high intensity UVA rays.
As far as the rest of the ingredients go, look for products that keep it simple and use high quality moisturizers like hemp seed oil, algae extracts, and aloe vera. Also look for antioxidant vitamins to combat free-radicals. Regular application of anti-oxidant vitamins to the skin not only inhibits ultraviolet-induced damage, but may also facilitate the repair of existing damage.