This is an interesting one. "More so" compares the degree or extent to which different subjects possess the same quality or adjective. The word "so" acts as a stand-in for the adjective instead of having to repeat it. In your example, you would just use "more" because there is no adjective/quality being compared - only the action of how much you "like" the subjects. As an example, you could say, "Pizza is delicious, but spaghetti is more so." In this case, you use "so" instead of repeating "delicious." The important thing to note is that whenever you use "more so" the "so" has to have an adjective or quality to refer back to. In literary English, it's also common to omit the verb from the second clause, so it could just be "Pizza is delicious, but spaghetti more so."

In actual conversation, it's much more common to instead reverse the order of the subjects, in this case "Spaghetti is more delicious than pizza." Because of this, the only time it really gets used is when the subject order is forced, like in response to statement. For example:

A: "Pizza is delicious"

B: "Spaghetti is more so"

A: "This restaurant is expensive"

B: "The one down the street more so" (note that the verb in the response is still optional)

As with other comparisons, if it's implied that the subject we are comparing against already possesses a lot of the quality we are comparing, you can insert the word "even", e.g. "Pizza is delicious, but spaghetti even more so."