Depends what other features you need. redis will be better if you need to do things like time-based collections, sorting by z-score, etc. Postgres gives you mature clustering (at least for master-slave), a mature tooling ecosystem (PgAdmin has been around for awhile, I didn't say it was good), better access controls, etc.

Like anything else in engineering, it's all a series of trade-offs to figure out what fits your needs the best.