The major upside is it will be easier to prove that you have product-market fit in your own backyard, for several reasons: you know your country best, no language barrier, costs will likely be much cheaper (smaller population, lower CPCs, etc.). The main downside is you won't have the same huge upside as you would if you gained traction in the US. I would highly recommend starting in your own country if you believe that will allow you to most quickly prove that people like your product / website. This is especially the case when you need momentum ASAP. Show an up-and-to-the-right growth trajectory, even if on a relatively small scale, and use the learnings and confidence to expand into new markets (and raise money if needed).