Pro-164 (psr-300)
The PRO-164 is the next revision of the PRO-97. They even look the same. You can read about the 164
here. The PRo-164 by Radio Shack is the same scanner, but packaged differently, as the GRE PSR-300.
You are really comparing two totally different animals. But it does depend on what you want to hear. If you're just listening to conventional stuff, then the '91 can be OK. If you want to hear trunked stuff, the newer scanners are a better way to go. Plus don't forget you can manage how these newer scanners are programmed with software on your PC.
ScannerMaster sells the PSR-300 for $149 and it comes with the AC adapter. RS does not include an AC adapter with the PRO-164. You can find these radios for a little less when on sale, or used.