Among aniline, 2-methylaniline, 3-methylaniline and 4-methylaniline, the weakest base in water is

The methyl group at the meta and para positions is electron releasing and increases basicity. An ortho substituent, whatever its electronic nature, lowers the basicity of aniline (ortho effect: steric hindrance to solvation and protonation of the anilinium ion). So 2-methylaniline is even weaker than aniline.