If you have time, hike this trail first, then go to the waterfall one; otherwise you'll probably be disappointed). It's a decent trail with a couple charming bridges and a sheep farm along the way, nothing spectacular. We didn't see any quetzales along the paved dirt part (this is end of May and the close of their mating season) and only went about 30 min into the actual trail.
I hear a lot of people start the trail at midnight to see sunrise at the top of the volcano. Make sure you don't freeze to death at the top waiting 1.5 hours for the sun to rise.
If you own or manage Sendero Los Quetzales (The Quetzales Trail), register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.