I am considering a multi-day hiking trip in Liechtenstein. Do I need to bring franks, or can I rely on euros?
Since you mentioned a multi-day hiking trip, my answer will focus on alpine huts. In other locations, most people accept Euros, but the exchange rate is most often quite poor. Also big grocery stores like Migros or Coop take Euros. Most restaurant in the pedestrian area in Vaduz and Schaan also take Euros, but more remotely located restaurant do not always accept Euros.
There are three major alpine huts in Liechtenstein: Gafadura, Sücka and Pfälzerhütte.
Pfälzerhütte takes Euros and calculates the prices in Euro on case to case basis with the latest exchange rate. The Gafadurahütte also takes Euros. Considering Sücka, I couldn't find any information, but I recall that I've seen people paying with Euros there. But I would contact the owners first and ask them.
In summary: Euros should be enough, especially if you also have a credit card. If you want to be sure that you won't be put on a disadvantage because of the poor exchange rates, I'll take Swiss francs with me.