Never had a problem with visa on arrival but I imagine it depends on your country of origin.
If from Bkk. Take the Nakon Chai Air VIP night bus and arrive Nong Khai in the morning.
Go have coffee and breakfast and use ATM if needing Thai money. Depending on the day and date of the month, the border crossing can be done in 30 minutes.
Take taxi or bus on right side of Lao border. I recommend a hotel near the Embassy if you are just visiting , if you have time , downtown riverfront is good fun and has many bars and restaurants.