Intro
Haikyu!! is a Japanese manga about volleyball, not a manhwa. The manhwa in the supplied list are unrelated to where you can read it, so they would make this guide less accurate.
Rankings
1. VIZ Shonen Jump — English chapters
VIZ’s official Haikyu!! chapter page marks its first three chapters free and later chapters as requiring access to read. Check the page for availability in your location. Our score for finding a place to start: 9/10.
2. VIZ — English collected volumes
VIZ’s volume catalog lists the English manga through its final volume. It is a useful starting point if you prefer collected editions. Our score for browsing editions: 9/10.
3. Shueisha — Japanese editions
Shueisha’s official volume list links to print purchases, digital editions, and previews in Japanese. Check each store’s terms and regional availability before buying. Our score for Japanese readers: 8/10.