The two poems present two completely different tones and experiences which draw from the experience of slavery. In a comparison essay, I might begin with a thesis something like this:
Although the speaker in "The Slave's Dream" reflects the deep injustices of slavery shown through a third-person narrator, the first person voice in "Still I Rise" encourages those impacted by slavery and racism to draw strength from the history of their ancestors.
In your question, you focus on two key words: empowerment and oppression. Angelou's poem definitely has a tone of empowerment. She uses words like "rise," "tides," and "hopes" to convey her unwavering perseverance. The repetition of "still I'll rise" throughout the poem and five times in the final stanza alone heightens the reader's sense of the speaker's strength. When she faces situations entrenched in racism where she is expected to bow her head or lower her eyes, she knows the history that guides her:
Bringing the gifts that my ancestors gave,
I am the dream and the hope of the slave.
The speaker's ancestors have gifted her with strength through their experiences. She is their dream. She is their hope. She can rise.
On the other hand, the speaker in "The Slave's Dream" describes the experience of a slave who suffers no such sense of empowerment. He lies with matted hair, half buried in the sand, his only hope of a reunification with the family he loves being provided to him in visions as he dies. The driver's whip beats him as his soul leaves the earth, but he cannot even feel the pain as his body is merely "a worn out fetter." The slave has been oppressed until he can physically no longer take the torture.
Both of these are experiences and voices worth hearing. Slavery in America was oppressive, and the descendants of slaves can draw strength from the stories and experiences of those who paved the road to freedom which they themselves never saw. There is both significance in honoring the experience of those oppressed ancestors and in becoming all that they dreamed of. The hope that burned within the dying slave in "The Slave's Dream" is the same hope that helps the speaker in "Still I Rise" overcome adversity.