All I can say is that I love my Aeris and budget permitting, it would be a 120 if I bought a shorter-travel bike 😉
I’m own the old Aeris and like the bikes. Recently demo’d the new 145 and 120 bikes. The the 120 is a quick bike. Pedals very well and descends better than it’s travel would suggest.
There is about 20mm difference in length (reach/ETT/wheelbase) between the Bird and the Scout in the same size. The Bird being longer. While the rear travel is almost the same the scout is designed to take a bigger fork. Also consider the different suspension designs give quite a different ride/feel. Try to demo both and see which you prefer the ride of.