For Khalid's research, the best method would be 4. Focus Group.
Focus groups allow for interactive discussions among participants, which can lead to deeper insights and feedback about their experiences with both Game A and Game B, as well as their thoughts on the new game prototype. This method encourages participants to engage with each other, which can lead to richer data and a variety of perspectives that can help Khalid's team refine their game.
While interviews and surveys can also provide useful feedback, focus groups are particularly effective for gaining qualitative insights and facilitating a collaborative discussion.