I live in Luang Prabang and am trying to maintain a few niche websites and blogs, etc. It is a bit more complex here for a few reasons.

The internet is slow at best. You can pay to get increased speed, but overall, the bandwidth is very low.
It is a slow place, a city in the middle of the jungle that is difficult to get into and out of (expensive flights even to Vientiane)
Vientiane is bigger and more business-oriented and has access to fast internet. It is also just a cheap bus ride across to Thailand, where you can access all of the modern amenities of the West.
However, all that said, I think that Luang Prabang is a lovely place to live and is easier going than Vientiane.
I love Vientiane a lot and love to visit, though.
If you manage to make it in the internet marketing game, most of these issues won't matter much, but if you are starting, I recommend Vientiane.