A COBRA participant has the right to keep their continuation benefits, even if they have access to a new group plan if the COBRA benefits are better.

What is a better benefit?

The DOL hasn't made an official definition, so "better" could mean a lot of things. However, usually it has to do with the financial exposure the COBRA participant has versus the other group plan and its premiums (like deductible risk, out-of-network providers, etc.).