El Camino is a movie that serves as an epilogue to the main series. It starts off immediately where the finale ends, and, if nothing else, provides some nice closure to several characters.
Better Call Saul, as I'm sure you're aware, is a prequel series centered around Saul Goodman. There is also a small percentage of it, plus the final couple episodes, that takes place well after the events in Breaking Bad.
I'd say all are basically on the same level of quality. There are even some out there that think BCS is even better than BB. I wouldn't go that far myself, but I'd say it is absolutely worth watching.