Over the years, I've had a lot of trouble with the old HO train set. In particular, it has been very difficult to get the track all laid out nice and straight and even, and it seems like there is always some joint that is opening up or has a bump that throws the trains off. This problem is particularly acute when trying to set the train up under the Christmas tree.
Last year, I made a wonderful base for it that I thought would cure the problems. It helped, but not enough. It was still tough to get a train around the track more than a few times without a derailment. So this year, I bit the bullet and bought Atlas Super-Flex track. It comes in three foot sections rather than the 9" sections I had been using - so 1/4 as many joints are needed. I did the whole layout (with more track than last year) with just 10 pieces of it. And because it is bendy, you can make more gentle curves than you can with the sectional track. It took me a bit of time to get the hand of how to trim it and how to attach the couplers (which I had to google), but once I got it down, it went quite quickly. So far the only derailments we're getting are when a very light car goes over a switch. I need to add some weight to some of the cars.
Haven't tried any very long trains, yet. It got dark as I was finishing laying the track, and I didn't get to hooking up all the electrical accessories (whistles, lights, switches) so I haven't gotten all the cars out yet as they'd just get in the way.