In that situation radar is more valuable because it is real time. The AIS targets can be delayed up to a minute from real time. Many times this is quite visible when you are viewing the AIS target on top of your radar. The two "targets" are separated due to this. I have the ability to view AIS targets on my radar screen and can see these differences. If it is a fast moving vessel there can be a significant delay on its AIS position and its actual position in tight quarters. Obviously, both are valuable, but you need to understand the limitations of each.