We cannot categorize sins by their relative importance.
They are all equally serious, because each is an expression of rebellion against divine sovereignty.
The difference between them–when one should or should not commit a transgression–depends on other factors, as was explained in regard to the Sabbath: “Violate one Sabbath for him, that he may observe many Sabbaths”. (Yoma 85b)
–Rabbi Adin Steinsaltz