"Travelling Laos in 2 weeks from north to central" Laos Things to Do Tip by seagypsy
Laos Things to Do: 298 reviews and 556 photos
I don't really think it matters which route you take since with only 2 weeks you're likely to enter/exit near VTE and exit/enter from Huay Xai. The only major consideration is that you'll be going downstream on the Mekong if you're taking the 2 day slow-boat from Huay Xai to Luang Prabang.
"I am more into nature than ruins."
BUT, given the above statement, you might consider taking a bus north from Huay Xai to Vieng Poukha and/or onward to Luang Namtha. Northwest Laos has become the major trekking destination for Laos BUT there are more areas than then northwest.
After a visit to the hilltribes trekking area, I would recommend taking the early morning bus from Luang Namtha to Udomxai (also known as Muang Xai/Sai) and heading east to Muang Khua, a bucolic rivertown where you can catch a slow boat down the highly scenic Nam Ou, which is far better than the Mekong boat journey .
YOu could even travel by boat all the way to Luang Prabang since the Nam Ou empties into the Mekong BUT it's quite expensive and requires a private charter. However, if you stop at the rivertowns of Moung Ngoi or Nong Khiaw, you're likely to meet other travelers wanting to share the cost of a boat to Luang prabang. It would recommend setting aside 9 days for the Huay Xai to Luang Prabang sector described above.
Two to 3 days should suffice for a great intro to Luang Prabang and I would highly recommend taking road transport between LP and Vang Vieng or Vientiane since Route 13 south from LP all the way to Vang Vieng is also very scenic, but also very winding, with some very impressive karst monoliths en route.