Try comparing them side-by-side if possible:
As stated above, the Bearcat is essentially a smaller Single Six with fixed (non-adjustable) sights.
The big question: if the Single-Six too big for you, or is the Bearcat too small for you? My dad has a SS, and I think it's great, but kinda bulky for a .22LR, and I never use that .22Mag cylinder it comes with.
On the other hand, for me personally, the Bearcat is a great, compact little piece. I'd much rather try and teach a new shooter with the Bearcat, and it is more likely to fit comfortably into the paws of children or the small-statured.
The Bearcat just came out in a stainless version this year as well, chalk another point up for it. Smaller and sturdier.