The clearest resolution of Haikyuu I’ve found is via the Jump Book Store (ジャンプBOOKストア). There’s a reader via web browser, and there’s an app in the App Store and Google Play for mobile reading.
You can preview part of the first volume for free. The screen resolution may be purposefully downscaled in the preview, idk.
All purchases via the Jump Book Store are for ebook versions, not physical. And for Haikyuu at least it’s sold in volumes (and sets of volumes), not individual chapters.
Also, ハイキュー・Haikyuu! 
Vol. 4+5 reading group ぜひ見てください 