It depends on your specific scenario.
Both behave slightly differently, depending on application. MOVs are sacrificial and even when they look fine, their performance still drops each time they've been called on to dissipate excess power. Depending on how they're placed in a circuit and how they are impacted by a surge event, they can sometimes fail in ways that leave the circuit live and unprotected and can even cause a fire during a thermal runaway event. TVSSs are longer-lived when used within their ratings, but any over-rating event can (similar to the MOV) result in the TVS diode fusing and leaving the circuit live and unprotected, potentially a hazard. If you're looking for longterm, rock-solid protection then I'd suggest looking at a Series Mode surge suppression solution. They're not cheap, but because of how they work (filtering the high frequency portions of the surge, banking and dissapating the low frequency parts) they only fail under the worst of conditions (test scenarios)... in short, they just work. Because of how today's electronics are built, using standard MOV or TVSS solutions can actually be worse than not using any surge suppression at all (depending on how they are implemented and how the system interconnects with other systems).
If your question is specifically aimed at a single circuit board (where you're just concerned about protecting it), then a multi-stage solution with TVS diodes, an overvoltage relay, and MOVs across all legs would probably offer the most preferable combination of protection. If it's one or the other, then I'd lean towards the TVS if your project is primarily data, or MOV if your project is power-supply related. Review the current UL standard (1449, V3) for info on how to combine MOVs with additional protection to reduce the risks of fire.
Quick Links:
