to be or not be~euro or dollars

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Drifter

I don't agree.
I've exchanged EUR in every major town in Laos, I've never carried USD. I prefer carrying Kip, if you want to buy something slightly more expensive, such as a flight or accomodation, use your credit card. If you're EUR based you're getting a very good rate. Using USD might help you a bit in the Mekong Valley (but even here Thai Baht are better) and Luang Pabang but otherwise there's no reason to have them, and no, they don't weigh as much as a brick either.
Go upcountry and they might not even know USD, it's not the local currency like in Cambodia.

I think, in my 40+ nights of accomodation in Laos, I stayed in one place (in LP) that accepted credit cards. Euro and dollars easily exchanged in major towns (and provincial capitals like Sam Neua and Phongsali), but not so easily exchanged in the small non-descript villages (even those on the bus lines, like Nam Noun).

Atms in Vientiane only.

Kip is preferred everywhere that isn't trying to aspire to westerners only.

Dollars! No ATM in Luang Nam Tha. I have a vague recollection of somebody thinking there was cash advance in LNT but only for visa, however I doubt this. Place isnt exactly massive.

ATM now in Luang prabang and Viang Vieng, doesn't accept visa though and very tempermental...

There is an ATM in Luang Nantha (I used it yesterday), but it only accepts mastercard and you pay 20000 kip comission. Visa cash advance is possible with 3% comission at the bank behind the ATM.