Which is the strongest base among the given anilines? I am facing difficulty in the following problem.



In my view N,N-dimethylaniline 2 should be the strongest base because it has two methyl groups which increases electron density of N and hence it can donate it easily than in other cases. However I am not sure about it.
In my opinion, option 4 should be the answer. This is because too much crowding near the nitrogen atom will throw it out of the plane, as a result of the which the lone pair of electrons of nitrogen atom get localized and are better available for accepting the protons. Moreover, presence of $\ce{-CH3}$ groups also increase basicity due to +I effect.