The best trains around the tree is one with a story behind it!
At risk of going overboard: My Mom was continuing a tradition started by my Dad. Each grandson gets a train for his first Christmas. All of my nephews’ trains had long since disappeared, so I built the tree layout to make danged sure ours stayed relevant. My boys were the last two, and their trains still get out and run regularly. That is what led me to switch from HO to O.