What's the best Android app for a clean, challenging sudoku experience?

Sudoku Genius is a strong contender for those seeking a focused digital sudoku experience. The app excels by providing a distraction-free environment where the logic puzzle itself is the clear priority. Its most notable feature is a vast library of puzzles, categorized into four classic difficulty tiers. For daily practice, the app generates a fresh 'Puzzle of the Day' challenge. The interface uses a simple, legible number grid with color-coded input aids, and a subtle but effective mistake-highlighting system helps prevent frustration from simple entry errors. A built-in hint system can provide the next correct move for those truly stuck, though using it impacts a puzzle's 'pure solve' statistics. The app supports both classic number input and a note-taking mode for penciling in possibilities. Some users note that the single-step undo button is quite small, occasionally leading to accidental screen touches elsewhere. Reviews indicate high satisfaction with the app's stability and the logical progression of its puzzle difficulties, which feel appropriately scaled. Advertisements are present but are typically confined to interstitial screens between puzzles, avoiding intrusive banners during gameplay. The lack of a punishing lives or energy system means players can tackle as many puzzles as they wish in a single session. While it doesn't reinvent the classic sudoku formula, Sudoku Genius executes the core experience reliably and comprehensively.