Zephyr Lodge in Lanquin is the best hostel in the area. Everyone stays here because its a one stop shop for all your backpacker needs. There is an incredible pool with mountain views, a restaurant/bar on site, hammocks, pool tables, nightly activities, and tours.
This hostel is one of those places that you can just lounge around all day and be satisfied. If you do want to get out and explore, they offer a fun tipsy tubing experience and a tour of Semuc Champey.
The mosquitos here are no joke so if you want to be protected, I would book one of the rooms with AC. I didn't do this and woke up with a face full of bites. Swollen eyes and all.
The only con to staying here is that its not near the town so you will most likely be buying all your food at the overpriced on site restaurant. Not ideal but if you only stay a few days its not so bad.