Which sulphate is the most soluble in water at room temperature?

The solubility of group 2 sulphates falls down the group because the lattice enthalpy of the large sulphate salts changes little while the hydration enthalpy of the cation falls faster. $\mathrm{MgSO}{}_4$ (about $35\mathrm{g}$ per $100\mathrm{g}$ water) is highly soluble, whereas $\mathrm{BaSO}{}_4$ is practically insoluble.