They are two completely different plugins by different authors. glN64() is an advanced OpenGL plugin while Glide64 is an advanced Glide plugin.
Which performs better depends on hardware. Lower-end cards (Worse than GeForce 2 or thereabouts) don't work very well with glN64() [If at all], whereas Glide64 will work better. Glide64 probably has the best compatibility with games of all plugins.
On a higher-end machine with a fairly powerful Radeon or GeForce, glN64() works better because it has no wrapper (and therefore no wrapper issues) and has better enhancements for the graphics, and hi-res framebuffer. glN64() is less compatible than Glide64.