I voted for uke
As uke you must trust tori to excercise control as they execute the technique. This trust is not always well founded, but it is the nature of Aikido that we train this way. Uke is therefore more prone to injury. Uke can do more to avoid injury by being relaxed and committed to their attack, and also by avoiding pre-empting tori's technique (in freestyle particularly).
Tori can do much to avoid injury to him/her self and to uke by excercising awareness and also taking a relaxed approach to the technique.