Margaret Atwood's best poem is almost certainly Siren Song: one of the best poems of the last fifty years by any measure. Helen of Troy does tabletop dancing is also very good.
Both are women's poems, but neither is really a feminist poem. Atwood feels her womanhood intensely, but doesn't usually see being a woman as a cause in itself. Margaret Atwood is primarily a human being, and writes for fellow human beings. A feminist poet tends to be a woman writing for women.
If you want a more aggressively feminist poet, you could look at the work of Carol Anne Duffy (particularly her sequence The World's Wife) or Rita Dove.
If you want seriously feminist writing, you should probably look at some of the work of Andrea Dworkin. Dworkin's work has a serious message, so she didn't write poetry (poetry is poor at delivering messages), but her work is incandescent with the feminist cause.
Dworkin's fiction is also appalingly written, and splutteringly nasty: but that goes with the territory.