Keep in mind that what you want may not be one font that covers lots of glyphs -- that makes the font take up lots more memory and take longer to load. And you definitely wouldn't want to use a high-coverage Unicode font as a dynamically-loaded Web font.
Operating systems are fine at understanding that different fonts are necessary for different glyphs, so what's better in a lot of cases is to have a family of fonts that together cover all the glyphs you need. That's what Google Noto [1] is doing.
Symbola is a good font for covering a lot of symbols, while not representing many text characters (on the assumption that you already have fonts you prefer for text).
That said, there's a justification for having a few of the fonts on that chart, like Lucida Sans Unicode and Arial Unicode MS, because they guarantee consistency without you having to install a huge font family. GNU Unifont is also interesting in a hackery kind of way, in that it achieves good coverage by using only pixelly bitmaps.
But on the other hand, Code2000 is an awful font. It eats gobs of memory and it looks bad. Don't use it just because it has a lot of glyphs.
GNU Unifont is just a fallback font, which I think is what the parent really needs since they're most concerned about seeing the symbol and I doubt consistent appearance with their font.
Operating systems are fine at understanding that different fonts are necessary for different glyphs, so what's better in a lot of cases is to have a family of fonts that together cover all the glyphs you need. That's what Google Noto [1] is doing.
[1] https://www.google.com/get/noto/
Symbola is a good font for covering a lot of symbols, while not representing many text characters (on the assumption that you already have fonts you prefer for text).
That said, there's a justification for having a few of the fonts on that chart, like Lucida Sans Unicode and Arial Unicode MS, because they guarantee consistency without you having to install a huge font family. GNU Unifont is also interesting in a hackery kind of way, in that it achieves good coverage by using only pixelly bitmaps.
But on the other hand, Code2000 is an awful font. It eats gobs of memory and it looks bad. Don't use it just because it has a lot of glyphs.