If staying and using the bus from Korat (city) I would consider 1) Bus or train to Ubon then International bus from Ubon Ratchathani to Pakse (Laos) 2) Korat to Mukdhan, then over the friendship bridge to Savannakhet (Laos) 3) bus or train from Korat to Nong Khai plus train over into Laos or over the friendship bridge onward short journey to Vientiane (Lao Capital)
I have used Aranya numerous times as my Thai address used to be Sa Kaeo (city) and only 45 / 50 mins away, last time in Poi Pet was getting a bus to Siem Reap, OK for looking at the casinos or onward travel, not good for staying in the city.
Was at Chong Chom / O' Smach border last year
Been over and stayed at all the others, Vientiane around 8 times (recommended)
Most trips were not border runs.