Chiang Mai or Luang Prabang?
 

We will be traveling to Thailand and Cambodia in February. We plan on spending in time in BKK, Chiang Rai and Siem Reap. We have 3 extra days in our itinerary. Should we include Luang Prabang or Chiang Mai?

Luang Prabang. If you have the time, you could even get the boat down river from Chiang Rai

LP, but it is quite expensive to get there.....book hotels now as they fill up quickly...

la residence is fantastic, imo....on the edge of town...

Luang Prabang, you will love the place.

Has anyone taken the boat from Chiang Rai to LP?

I'm in Chiang Mai now, just flew today from Luang Prabang, which I LOVED!!! I talked with a couple who took the boat from Chiang Rai to LP and they enjoyed it but said it got a little "boring".
On my current trip report, I raved about Mekong Riverview Hotel with a link.

I did four flights on a Bangkok Air discovery pass -- total cost about $500. Bangkok to Siem Reap, Siem Reap to Luang Prabang, Luang Prabang to Chiang Mai, and Chiang Mai back to Bangkok. If you haven't arranged your travel yet, it's a great way to do it.