When should I use `publishReplay` vs `shareReplay`?

shareReplay() is basically publishReplay().refCount()

Definitely not.

Both shareReplay and publishReplay (+ calling connect on it) will make the observable behind it hot.

But the very important difference between them is:

• shareReplay: won't stop emitting until it's completed, no matter if there are no subscriptions anymore or not.
• publishReplay: will stop after the last subscriber unsubscribes if used together with refCount

Imho this is a crucial information.

publishReplay allows you to controls when the subscription starts. shareReplay will start automatically upon the first subscription.

Generally, if the observable is to be used in a template (html file) use shareReplay. The advantage being you won't have to worry about unsubscribing etc.

shareReplay() is basically publishReplay().refCount()

Here is a great article explaingin just that in detail: "Angular Async Pipes  - Beware the share"

Edit:

The right thing to say is:

shareReplay() is similar to publishReplay().refCount()

see @DevRok's answer for more info why they are not exactly the same.