I thought about this for a bit. For me its the changing of seasons. There's something beautiful and powerful yet simple about this cycle. Its one of those things that remains a constant part of your life, even if you don't realize it.
I agree, it's a wonderful thing. It gives life a rhythm and those times between two seasons can be really electric. You can literally feel the world changing, you can smell the change etc. It's an amazing phenomenon.
Without question, Fall. I grew up in Michigan and Fall there is gorgeous. I love October in Michigan, I have spent many autumns in Northern Michigan on Lake Charlevoix, looking at this:
Also because every high-school crush I had was Fall themed, heh.
Fall is a great time for romance. Need to find a warm body for the impending winter.