Depends upon what you want to do with your new rifle.
The GSR is more versatile. The only reason for a 77/357 (other than to just have one, which is always a good reason to own any firearm) would be to hunt deer or hogs in a state that doesn't allow traditional centerfire rifle hunting for them, but will allow it with a rifle chambered for handgun cartridges.
A GSR is on my "to do" list.