Neither. They used to think that a tidally locked planet would be like that. But recent research shows that if it has an atmosphere, you get thick clouds forming on the sunny side which block out the heat, and the atmosphere keeps the planet warm on the cold side. As a result, red dwarf planets in the habitable zone, like the planet candidate for Proxima Centauri B, which used to be considered uninhabitable are now thought to be quite likely places to find life - especially since there are many more of them than there are sun like stars. It just needs a few percent of them to be habitable to get vast numbers of habitable planets.

This shows how the clouds would form on the sunny side (clouds in white) in a map of a tidally locked planet around a red dwarf star.

These clouds provide 73 degrees C of cooling, so permitting the planets to be far closer to their host star and still be habitable. See Red Dwarfs: Clouds in the Habitable Zone and for the paper itself: Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets

We could check this by observation once we can see the planet itself as a distinct point of light, as in the infrared it will be coldest on the sunny side, unusually, because of the high clouds, and warmest on the night side where you can see right through to the surface, an effect we also get on Earth where Brazil for instance, when covered by clouds, seen from space in infrared, can seem very cold because you are measuring the temperature of high clouds.

As well as that you can get planets that get into 2:3 resonances like Mercury through tidal effects, where its spin is two thirds of its orbital period, as a result the day on the planet is actually two orbital periods. For Proxima Centauri planet that would mean a “day” of 22 Earth days if it is in a 2:3 resonance.

So red dwarf planets are top candidates now in the search for life in our galaxy.