In a rare case these past few years of Konami being proud of their history, Pixel Puzzle Collection is a solid Picross game. It's free with only minimal advertising and has some neat quality-of-life features like auto-filling in "X" markers when you complete a line.
If you like Picross at all, even without the Konami nostalgia, this is well worth checking out.
If you like Picross at all, even without the Konami nostalgia, this is well worth checking out.