RE: Which of these two ST?
What are your intentions? The AE t4.1 would make a more competent racer than the HPI, IMO, and the HPI would be better suited to bashing. Not saying wither one is worlds and worlds better at one or the other, but respectively that is where I think they stand.
One thing to consider is are you going to be ordering more parts online, or skipping the shipping wait times and going to a LHS? I would honestly pick one or the other based on what my LHS sells more parts for, as they are both very competent in their class.