Some quick reading has led me to understand the following. Please correct me if I'm wrong.
ADS-B is GPS based. The target's GPS position is somehow transmitted to your aircraft. I assume that under this system, bearing information would be far more accurate than TCAS.
TIS is a technology based on Mode S. A suitably equipped "Mode S" radar site is involved in the data transmission.
Am I correct thus far? If so, here's where I'd still favor TCAS, but will be content if ADS-B used in lieu of TCAS:
TIS uses Mode S technology. I assume most new transponders are mode S capable, but it is still not the standard worldwide, or in the US. I *believe* that mode S is the standard in many parts of Europe. Furthermore, according to
this link, the FAA is discontinuing the TIS program. Possibly in favor of ADS-B?
ADS-B is satellite based, and so is not an independent system. It didn't explicitly say GPS, but if it's anything similar to GPS, then they can pull the plug whenever they wish, and it may well have serviceability issues (think RAIM).
Notwithstanding, I'd still be fine with everybody having ADS-B. But I wonder if the responses would be different if the thread title had ADS-B instead of TCAS.