Which is the correct order of basic strength of methylamines in aqueous solution?

In aqueous solution the standard order for methylamines is secondary > primary > tertiary: the $+I$ effect raises basicity from 1 degree to 2 degree, but the tertiary ammonium ion is poorly solvated (fewer N-H bonds for H-bonding) and sterically crowded, so $(\mathrm{CH}{}_3){}_3\mathrm{N}$ falls below $\mathrm{CH}{}_3\mathrm{NH}{}_2$.