Basicity of amines depends on the availability of lone pair of electrons on nitrogen for protonation.Ethyl amine is stronger base because the alkyl group is electron donating in nature, thus it increases electron density on nitrogen.

Aromatic amines(for ex. aniline) are less basic than aliphatic amines due to

1) resonance in aniline- the lone pair gets delocalised over the benzene ring and is less available for protonation

2) lower stability of the anilinium ion than aniline; aniline is resonance hybrid of five structures while anilinium ion is resonance hybrid of only two structures.

For these reasons niline is weaker base than aliphatic amines.