Man, I spent ages hunting down a reliable place to watch 'Naruto: Shippuden' episodes online when I first got into it. The best legal option is definitely Crunchyroll—they’ve got the entire series, subbed and dubbed, and it’s ad-free if you spring for premium. Hulu also carries most of it, though their catalog shifts occasionally. If you’re outside the U.S., Funimation might be your go-to, but they merged with Crunchyroll recently, so things are still settling.
For free (but legal!) options, Tubi and Pluto TV have rotating selections, though they include ads. I’d avoid shady streaming sites—not only are they unreliable, but they also don’t support the creators. And if you’re a completionist, the Blu-ray collections are worth it for the extras alone—commentaries, art books, the works. Happy binge-watching!