The Amazon Fire HD tablet can be a good option. It's relatively affordable and has decent display quality. Plus, you can access a wide range of manga apps on it easily.
I'd recommend the Samsung Galaxy Tab S series. Their sharp screens and powerful performance ensure clear and lag-free manga viewing. Also, they offer good storage options to hold a large manga collection.
The iPad Pro is a great choice. It has a high-resolution display and long battery life, making for a smooth manga reading experience.