I have flown every Chrismtas Day from EWR - BUF since 1986, and since CO went with EMB's on the route, I have always had 1A. I generally tip them becuase it's Christmas, and I sit near them during taxi, etc, and they are almost always very friendly, and I feel bad for them working on Xmas. They have all accepted the tip in the past!
Last Xmas after my arrival in BUF, she had to fly back to EWR, and then to Manchester NH.......I thought is was a nice thing to do for her.