Riding in a Talgo sleeper was pretty uncomfortable, but I'd take it any day over flying.
My actual worst train experience:
On a train from Warsaw to Lublin, I got up to use the bathroom and forgot that my earphones—the ones I had saved for two months to afford—were in the pocket of my oversized shorts. After figuring out how to open the restroom door (it was remarkably difficult on this Soviet-era carriage), I entered and the train went into emergency stop (or something similar). I immediately grabbed the only handle I saw: that of the door. I couldn't get the door open again, but that wasn't my primary concern; I really needed to use the facility. As the train started to move again, I loosened my shorts and felt something run down my leg. I looked down in time to see my earphones and all my European currency fall out through my shorts and drop through the hole in the floor that I hadn't previously noticed. Not pleasing.
When I tried to flush the toilet, part of the rusted handle broke off. The sink water was very cold and very brown. It took eight kicks to get the door open, and I'm pretty sure I broke it, as it wouldn't shut again. Not pleasing.
I was looking forward to seeing Lublin, which was supposed to be an interesting and historic city. I figured I wouldn't let my experience on the train sour my day.
Got to Lublin, got in a cab, my uncle said something to the driver in broken Polish, and we were driven through a decent-looking neighborhood to a large park. The cab stopped, the driver said something to my uncle, and we got out. The park seemed to be a large, empty field with a monument and a few buildings at one end. Intrigued, I walked closer to the buildings, and upon inspection determined that they were barracks of some sort, and that one building seemed to have a small chimney. From history classes and a horrible conversation during a seder, I knew my rail trip to this place had been significantly more comfortable (and survivable) than many others', but a concentration camp is still no way to impress tourists.
After walking around other parts of Lublin, we headed toward the train station because we figured there'd be food nearby. Went into a restaurant, my uncle said something to the waitperson, received bowls of what looked (and, I believe, tasted like) blood. I ate/drank mine, assuming it was simply salty beet soup. Then we got pierogies. Took a bite of one, and whatever mammal was inside was not fully cooked.
The train on the way back was a little bit better, and it had a diner. Figuring the food couldn't be worse than a bloody dumpling, I ordered what I thought was fried chicken. I was brought a large piece of fried processed cheese with a side of mayonnaise. Amtrak food really is quite good.
Lesson: Don't use the bathroom on a s***** local train in Eastern Europe. Better yet, don't visit Eastern Europe.