I agree, it's hard to choose!
Sight because I am one of many that find myself looking at every light display when I'm driving in neighborhoods to admire their displays.
Smell because who doesn't love the smell of a fresh Christmas tree, not to mention the holiday baking!
What about sound? The Christmas songs, jingle bells, or hearing the infamous "Ho, Ho, Ho" phrase?
Whatever sense it may be, it still makes it my favorite time of year.