The one-way ANOVA is used for between-subjects designs with separate groups, whereas the repeated-measures ANOVA is used for within-subjects designs with the same participants. A key advantage of the repeated-measures ANOVA is that stable individual differences are subtracted from the within-groups variance ($MS_W$), leading to a lower $MS_W$, a higher $F$-ratio, and a more sensitive test compared to a one-way ANOVA where these differences inflate the variance.