I understand the newest version of ARC8 includes support for the RR web import, something Scan Control can't do. It uses a proprietary copy/paste method to get data from RR that doesn't require a subscription.
On the other hand, if you have more than one receiver that SC supports, then you save some money. However, the author has not yet updated the program for the XT scanners, and has stated on his Yahoo group that he doesn't have the resources to do it right now.
Personally speaking SC was nice in its day, but it reeks of a early Win95 era design. I don't like their editor at all, and some users (including me) have noticed that the program is unstable; it tends to crash at the wrong times (doesn't it always, hi)
If it were me, and all I wanted to use the software for was a BCT8, then ARC8 might be a better choice.