I'm flying into Bangkok in February and at this stage plan to fly directly to Luang Prabang the next day to save myself some travel time.
Regarding cost and reliability, would it be best to book my flight once I'm in Bangkok or book ahead on a site like skyscanner?
Any suggestions would be greatly appreciated.
Definitely cheaper to book ahead, but it's going to be expensive either way as none of the budget airlines fly that route. Bangkok Airways will probably be the cheapest - compare prices on their website (www.bangkokair.com) with online booking sites. Alternately you could fly straight to Vientiane for significantly cheaper with Lao Central (www.flylaocentral.com) or Udon Thani cheaper still with either Air Asia (www.airasia.com) or Nok Air (www.nokair.com), and take a bus up to LP from either of those places. Not a short bus ride by any means but would probably save you upwards of US $100.
Thai Smile (part of Thai Airways) begins direct Bangkok - Luang Prabang flights December 15, 2013 (tomorrow). So at least now there will be another (possibly cheaper) option. Check for fares http://www.thaismileair.com
February is still pretty busy on this route. You won't likely get cheaper airfares booking locally so if you know your dates book online beforehand.