Note: so far, I watched the Defenders Season 1 and I am currently watching the first season of Jessica Jones. I will edit my answer as I progress in the show. I didn't plan to finish watching Luke Cage past the third episode.
tl;dr: Jessica is consistently shown to be stronger than Luke Cage.
Let's take a third character as a reference before comparing Luke Cage and Jessica Jones:
Daredevil in a fight
Daredevil, alias Matt Murdock, is strong, athletic, and agile. He also trained to fight with the help of Stick. He is definitely stronger than an average man but he is not seen as being beyond human limits. As a proof, we can see him struggling during his first fight on the dock (Season 1 Episode 1), and he spends the next episode recovering. He got better as the show progresses, able to take on several opponents, but he is systematically seen panting and exhausted by his fights. More importantly for our comparison of raw strength, after a few seconds lying on the ground, most opponents get up for a second round. It takes several blows to eliminate an opponent.
Luke Cage in a fight
At first sight, it is clear from Luke Cage and his tight T-shirts that Luke is fit and spent some time body-building. He was probably already way above average, probably stronger than Daredevil, but not beyond human possibilities, before the experiments that gave him.
In a fight, for example the one in his bar in Jessica Jones Season 1, Luke is able to knock out most enemies in one or two blows. I would argue that his unbreakable skin gives him a slightly supernatural strength: it is quite common to break one's fist when punching someone, but Luke Cage does not have this problem, and can hit people tirelessly with all his power. He also seems to not be easily exhausted.
Jessica Jones in a fight
On the other side, Jessica seems to be a frail woman. But her superpowers give her a strength far beyond human limitations. In a fight, she can effortlessly eliminate any opponent in one blow.
We can also witness her strength in Jessica Jones' sixth episode of the season 1 when she lifts a big man with one arm to interrogate him. In the pilot episode, she also stops a running car with her bare hands.
Here is a video of the fight scene in Luke Cage's bar:
Note that he is surprised by her strength.
Conclusion: at this point of the analysis, it seems that Jessica has the advantage on the question of physical strength.
Luke vs Jessica
I am aware of only one altercation between the two lovers in the Marvel Netflix Universe. This happens at the end of the sixth episode of the first season of Jessica Jones. In this episode,
Luke Cage learns the name of the bus that supposedly killed his wife. Jessica, aware of the whole story, knows that the man is innocent and tries to stop Luke.
While Luke is walking towards the bus driver, Jessica tries to stop him with her two hands. But this does not stop Luke. I find it quite inconsistent, considering Jessica had lifted men with one hand in the past. Sure, Jessica does not want to hurt her friend, but she is determined to stop Luke before a catastrophe arises.
The scene (you can stop after 30 seconds if you want to avoid spoilers):