I've done both and unless the prices are close, I'll usually take 2nd class. There isn't a huge difference in seats. The only time I wished I took 1st class was on a train from Bratislava to Budapest where they oversold tickets so the train was out of seats. I honestly didn't even know I booked 2nd class at the counter, just took what the clerk gave me. Lots of backpackers crowding things, but was lucky enough to grab a seat in the dining car otherwise it would have been miserable.