Love that stretch of train to Ubon. Very bare and etherial landscape.
'Can't recco the new Laos train. Hard, thin seats, squat toilets. Massively packed out with Lao people so you need to book in advance (in cash, pristine bills only). Myanmar wins it for old trains through beauty.
I'm sorry to see that a lot of day train options, partic going south, have been cut back. I did the jungle railway down to Singapore twice. It's a lot less jungle-ish these days.
Best long distance bus ride: Hue to Vientiane. 24 hours back in the day.