In water, aliphatic amines are generally more basic than ammonia due to +I effect of alkyl groups. Among lower amines, secondary amines are often strongest in aqueous medium because they combine favorable +I effect with effective solvation. Aniline is least basic here because the lone pair on nitrogen is delocalized into the benzene ring by resonance, making it less available for protonation. Therefore the order is dimethylamine > ethylamine > ammonia > aniline.