I looked at and test drove both before I bought my Agility. At first glance, they look quite different. But, once you are in the saddle, the only real difference is the fit. Both bikes are well built and have zero plastic squeak. I really didn't find the Super 8 all that more stable. No better or worse than the Agility under 45mph to be honest. The foot position is a bit different on the Super 8 with those foot "cowls" which are kind of nifty, and it does sit a bit more upright. But, other than that there wasn't much difference.
Save for one bit: Money.
OTD the Super 8 ran about 2700. The Agility ran $2135. It may not seem like much, but that was the utility deposits for our new apartment. So, with all else being equal, we went with the Agility 125.