That's a tough choice! Both dates have their pros and cons for weather. Late September usually still has some warmth lingering, maybe sunny days but cooler evenings. October, on the other hand, definitely leans towards being cooler and potentially wetter. It really depends on what you prefer. If you enjoy outdoor activities, maybe the slight gamble of warmer weather in late September is worth it. I remember trying to play the Slope Game outside last October and it was a little too chilly after a while! I would lean towards late September, personally, for a better chance of enjoying the sunshine. Have fun on your trip!