Chandi is an aspect of the Great Goddess that controls everything sentient, so it certainly does influence even the planets. A form of Chandi (called Vanadurga or the Goddess of the Forests is specifically known to influence planets in favor of those that invoke her energy).
However, Navagraha Homa in some cases might have a faster effect, especially if you know you have a negative planetary position.
I would say go with your gut. If I had to pick only one of the two, it would be Chandi as there is nothing she cannot accomplish. It is also one of my Top 3 mantras for precisely that reason.