r_textureMode cvar has four settings. Generally, you'll only want
GL_LINEAR_MIPMAP_LINEAR, which applies a linear filter to both the texture and the mip levels (?).
However, I personally like the look of
GL_NEAREST_MIPMAP_LINEAR, which shows the hard edges of the pixels, but still blends the mip levels.
LINEAR means linear filter, which blurs linearly between pixels and mip levels.
NEAREST means nearest neighbor, which keeps hard edges between pixels and mip levels.
GL_ is the texture filter,
MIPMAP_ obviously applies the specified filter between mip levels.