This border crossing is maybe one of the most fickle, either way, some days its trouble-free others it's a no go. If you're exiting from Cambodia I would suggest Osmach into Thailand if you intend to then go to Laos, but that brings its own set of problems with permits to enter Thailand. Nong Khai is your best option to enter Laos, but again it can be hit and miss regarding trouble free crossings and you may have to pay a tour agent fee.
Maybe Blackwolf can give your more as he has had recent experience.