Considering the basic strength of amines in an aqueous solution, which one has the smallest pK b value?

Since in aromatic amines the lone pair undergoes delocalisation, aliphatic amines are more basic than aromatic amines.
$\mathrm{Ph}-{\mathrm{NH}}_2<\mathrm{R}-{\mathrm{NH}}_2$
In an aliphatic amine, due to the $+\mathrm{I}$ effect of $-{\mathrm{CH}}_3$ the order will be $3°>2°>1°$.
In an aqueous solution, $\mathrm{H}-$bonding takes place. So, the order will be $1°>2°>3°$.

However, the resultant basic order is due to a mixture of both the effects($+\mathrm{I}$ and hydrogen bond). So, the order is $2°>3°>1°$. 

So, the final basic order is