I would think RF Signals would be the way to go
Why?
RF direction finding is very difficulty.
Even Kevin Warwick went for IR when he was going to run a half marathon with one of his robots.
Unfortunately, on the morning of the race, the robot locked on the strongest source of IR and set out for it.
It didn't manage to achieve escape velocity (I don't think the batteries would have lasted until it reached the Sun anyway) and crashed on the other side of the car park.