I'd recommend Tachiyomi. It's a popular choice among manga readers. However, make sure to download it from a trusted source as there might be unofficial or modified versions that could pose security risks.
Mangatoon is worth trying. It has a decent collection and provides a smooth reading experience. Some of its features like bookmarks and recommendations are quite handy.
Tachiyomi could be what you're looking for. It's customizable and has a lot of sources for free manga. However, it might require a bit of setup to get it working just right.