I don't know that I can specifically name a particular "worst" scanner ever, but I kind of chuckle at the TRX-x and the Pro-197 mentions.
I have a TRX-2 at home that works just fine on the MPSCS system, smack dab in the middle of a simulcast tower county, it doesn't miss a single transmission. I have 3 WS-1080 (a-la GRE PSR-800's) in use between Macomb county and Washtenaw county, both simulcast counties. Work great. I have 2 Pro-197's in service, one works fantastic, one does not.
The difference for the 197's where one works, one does not? Antennas. I've combed the threads here, followed the insights of many well regarding folks here as SME's and put a ton of energy into the antenna systems that these radios all operate on. I guess I just chuckle when radios get dinged for the dreaded simulcast demon as being the worst ever.