If we have any money to spend, I would prefer we first buy a proper LWB. Maybe Gosens. That will have the biggest impact on our starting XI quality, and this position should be priority for upgrade.
If we have money left over, I would prefer a midfielder over vice-Lukaku. Vidal ain't reliable anymore (lets see how he does when he comes back), while Sensi is never fit. So we don't have quality rotation for our 3 starting midfielders. For our 2 starting strikers, at least we have Sanchez. So I would rather spend 30m on Locatelli than Muriel.
If the above two issues are somehow sorted and in the unlikely event we still have money to spend, then Muriel could be a decent option for 30m. But there are also rumours that Belotti is forcing his way out of Torino this summer and could be available for as low as 35m. Between the two, I would prefer Belotti.