I understand buses to Phonsavan take about 8hrs from either Vang Vieng or Luang Prabang.
Is one of the routes more scenic than the other?

I would say VV to Phonsavan is more scenic because of the first part but not much difference as they are the same road for the last 4 hours. Think VV to Phonsavan is only 6 hours, LP to Ph. is 8 hours by bus, thats assuming you don't get a puncture.
Edited by: Herbie47
As #1 says. Its the same road on is just further away than the other. Either way its fairly scenic.
So if I head to Phonsavan from VV & then hang a left to LPB where the road joins will I get the most scenic route from VV to LPB?
Thanks, Herbie & Dog, it seems then that both journeys use route 13 and turn at Phu Khoun.
My map shows a road a little to the south of Vang Vieng, at Ban Tha Heua, heading east to Saisombun then turning north to Phonsavan. The road is marked 'dry season only' and I'll be there in late January - do you know if this would be an interesting route to try?

Could be interesting but don't think buses will go that way, not sure how you will go that way.

I've seen that road near Ban Tha Heua as it turns off Hwy. 13 going east & this map has it at km 130 - http://hobomaps.com/Hwy13LowerMapLaos.html. A sign at the turnoff says it goes to Nam Ngum. I've never taken it so I have no idea where else it may go. I think Nov. qualifies as the dry season.
@Herbie47 I'll be on a motorbike.
Speaking of maps, these topographical maps are the most detailed. Not easy to navigate directly from the website: either too small or too big, but if you save the page & open in your PC's viewer you can zoom to any magnification.
http://www.explo-laos.com/Explo-Laos/Cartes_%28en%29.html
Edited by: farengi