Exothermic dissolution
There is no easy general pattern.

The dissolution can be formally divided into 2 steps:


breaking the ion lattice into free ions in vacuum
hydration these "naked" ions by water.


Both lattice forming and hydration enthalpies are negative and their absolute value increases with increasing ion charge and decreasing ion radius.

The relation of their values and the overall enthalpy sign  depends on the particular element chemistry, that modifies hydration and lattice enthalpy values.

There are some trends, but hard to generalize. 

You can compare sodium and potassium salts of big anions with delocalized charge, like $\ce{NO3-, ClO3-, ClO4-}$. Dissolution of respective potassium salts is significantly more endothermic, compared to sodium ones. Sodium ion is smaller and is more intensely hydrated with lower enthalpy of hydration. 

This difference is bigger that difference of their lattice enthalpies. It is probably due anion size,  packing of bigger potassium cation makes less difference than for chlorides.