[ferbivore]

Drawing one quad to cover N characters and picking out a glyph in the shader is going to be faster than drawing individual quads for each character (for monospace fonts, anyway). But there are only so many characters you can fill the screen with, so it's probably not a huge difference in practice.

Regarding the upload part: at the end of the day, you have X bytes of glyphs and they need to get into GPU memory somehow. Whether you get them there as textures, as uniform data or as shader constants doesn't really matter performance-wise. If anything, doing it through shader constants as described in TFA is more expensive on the CPU side, since all those constant declarations need to be processed by the shader compiler.

What does matter on the GPU side is which memory hierarchy you hit when reading glyph data (texture fetches have a dedicated L1 cache on most GPUs, larger than the "normal" L1 cache I think) and what order the data is in (textures are usually stored in some version of Morton order to avoid cache misses when you're shading blocks of pixels). For a production atlas-based text renderer you probably want to use textures.

Edit: I misread the question; you were asking about drawing individual glyphs on the GPU vs. drawing an entire block of text on the CPU, right? This is a speed/space tradeoff, the answer is going to depend on how much memory you want to blow on text, whether your text changes, whether it needs to have per-character effects applied, and so on.