It is not a case of better, but choice. The Aerorest must shot 3 vanes, and it is easier to set up. A QAD can do all van configurations. It also need some set up in order to shot right. For maintenance, AeroRest is simpler, but for those who know their equipment, there should be no issue. It is a proven set up. AeroRest is not out yet as of today.
To add to what Dorge has already stated, let me add my two cents worth to this thread. If you are an occasional shooter, you might want to think twice about changing your current rest. If you are certain you want to make a change, but don't have the time to undergo a lot of retuning and testing, then stay with an easier choice.
The QAD Drop Away Style Rest has many good qualities and advantages over the factory Whisker Biscuit, but it does take patience and time to get it aligned and tuned to your crossbow, so you might need to expect the performance not to be perfect for at least two or three weeks as you work through the steps. In the end, it eliminates the need to ever replace anything on your rest again, but until you achieve the correct alignment your shooting accuracy will drop off.
The ability to shoot three or four vane arrows does not seem very important to me, since I have both, but can't say that either configuration of vanes is more accurate than the other.