I want to find out more about both how each of the independent variables is related to the dependent variable, but also how the two independent variables interact. If for instance motivation is more of a factor in one ability group than the others.

Should I do a ancova analysis with the continuous variable as a covariate or rather a two-way anova and group the continuous variable into categories (highly motivated, average motivated etc)?

What are the advantages of ancova vs anova and vice versa in this case?