Ethanolamine (C\(_2\)H\(_5\)NH\(_2\)) is the strongest base in aqueous solution because the ethyl group (C\(_2\)H\(_5\)) is electron-donating, increasing the electron density on the nitrogen atom and making it more basic compared to phenylamine (C\(_6\)H\(_5\)NH\(_2\)), where the phenyl group withdraws electron density.