Border open 8am-6pm. Can be busy mornings when most people cross and head for the slow boat. Join the crowd and make some travel friends or go your own way. Can get a bus to Luang Namtha in 3-4 hours or all the way to Luang Prabang in 14-16 hours.
See travel info here.
How much time do you have for Laos? If a month go explore the far north more but if 1-2 weeks then get to LP, maybe side-trip to Phonsavan, Vang Vieng, Vientiane. If you're headed to Cambodia next allow a week or so for southern Laos, i.e. Don Kong or Don Det, Wat Pu, Bolaven Plateau, etc.
But I have heard so much horror stories about the slow boat that I think another transport option would be much better. Will there be buses from the borders direct to Luang Prabang?
I only have 16 days in Laos. Still not sure if I should head down in southern laos or cross back over to Thailand to get to Cambodia.
What "horror stories"? The slow boat is basically you and 50 or more people floating downstream for two consecutive days 6 hours each. You get out at Pakbeng halfway and find a guesthouse and carry on the next day to LP. For some it can be boring or a bit too cattle-like, but for others it can be peaceful and scenic. Depends on attitude/patience and how much you like being lumped together vs. independent travel.
There are direct buses from Huay Xai to Luang Prabang. Schedule here. ("Bokeo" = Huay Xai)
Southern Laos is nice, but might be rushed with 16 days total. The usual route through north Laos usually takes 7-10 days then could grab an overnight bus from Vientiane to Pakse and still have some time for the south.
well, mate, the slow boat trip is one of the highlights of many people who have tried it. please read the following thread especially the most recent posts written from late 2012 till 2013:
Most of the horror stories about slow boat are out of date, I don't think it is that much of an issue anymore. To me it was ok but nothing overly special, kind of like being on a loud airplane ride(individual seats and noisy so tough to talk and meet people) with nice scenery. Just note to avoid the back of the boat as some engines are very noisy. If you do want to meet and chat with others your best bet is to sit on the floor at front of the boat but then you won't be quite as comfortable.
If I were to do Laos again I would try the bus route to Luang Namtha, Udomxai, Nong Khiaw then boat up to Muang Ngoi and then boat down to Luang Prabang . The Nam Ou river was more scenic then the big muddy Mekong(I only saw it from Nong Khiaw to Muang Ngoi though) although the boats used only have wooden seats so aren't as comfortable.
If you do the Mekong trip and for some reason want to try the speedboat(I think it would be a blast) it wouldn't cost too much more to take speedboat from Huay Xai to Pakbeng and then slowboat to Luang Prabang, note this would still take 2 days. The river from Huay Xai to Pakbeng is pretty smooth and I don't see it being unsafe, Pakbeng to Luang Prabang was a little rougher water in places though.
As for other tips on the border crossing, have USD with you for visa, they rip you off on exchange rate if you don't(this is the same at most border crossings in SEA). Pictures are nice but they only charge you an extra dollar if you don't have them.