You will almost certainly not place in academia in the econ program. And while it's easy to get a reg monkey job out of top econ jobs, the interesting positions are competitive. Outside options are still way better for econ, but not amazing.
I'm not sure what you mean by "excellent", but I would only go if it's in the top 10. Outside options decline much more rapidly in poli sci. Advisor matters a lot too. Do your research and figure out who you would want to be your advisor, then check their placement rate (not the programs). Good advisors at top programs place >70% of their students.
Keep in mind the substance varies A LOT across these two disciplines so make sure if you go for poli sci that you're substantively interested in some of the research topics. If you find you don't like the material it's going to be hard to motivate enough to write a good diss.