If you want to perform DFT seriously, priority should be given to the accuracy or reliability of the calculation (my opinion!). I think the more convenient approach to classifying the packages as licensed (purchasable) and open source (free to use) rather than best and simple. Among the licensed packages, I can recommend VASP, which will give you authentic results.

Thanks

I agree with Somnath, the VASP package provides reliable simulations for a wide range of material properties. An alternative free option is Quantum ESPRESSO. Nevertheless, if your Institute or university possesses the necessary licenses, the most user-friendly software would be Materials Studio, which includes the CASTEP package.