I would say space and time, for the reason that they are the only ones without limitations. For the upcoming war all of them are good, but after I only see these 2 with infinite possibilities. Time can help choose the correct path in explorations, warn against traps and instant death scenarios, it can also help steer a conversation in the direction you want or help in heists against surprises. Space can do many things aswell noted in other comments. The others can be weakend or nullified from the opposite element.