Analysis of the corners:
Upper left: the move at Black 18 (a) is forcing but the exchange of the stone in the corner for a stone in the center is perhaps more favourable for White at this stage.
Upper right: the region where White reigns at the moment. Requires reduction.
Lower right: Black lives small and White has some forcing moves there threatening to enclose the right side.
Center: White has a useful but weak group.
The upper side is low, so I think that the most promising plan is connected with the hasami on the right side. But the magari at 1 is too painful. I'd play 1 hoping to scare my opponent to extend. Pushing along the sixth line is a bad thing but Black has a lot of moves that would reduce White's territory at the bottom.