优秀 (yōuxiù) is the most common, all-purpose word for 'outstanding, excellent' — used for people's performance, character, or work. It's broader than 出色 (chūsè, 'remarkable, standing out') and 优良 (yōuliáng, 'fine, high-quality', often for products or conditions). 优质 (yōuzhì) specifically describes the quality of things, not people.