The noise...but that's what you get if you want to be central! :)
I stayed at this hostal for 6 nights, and I couldn't have asked for a better place to stay. I had booked a 4-beds bedroom, but I arrived with a massive cold&flu, so the staff kindly allocated me in a room for myself with my own WC. And they let me stay there for the rest of my journey so that I could recover and not bother other guests - at no extra cost. This was extremely kind of them, and much appreciated for sure. Additionally, the staff was super friendly and helpful with all the info you need to get around and go to local places for shopping and food - a special thank you to Sr Juan, for the lovely evening chats, his recommendations, and for caring.
The Avenue Hostal is actually being refurbished, so the hostal being used is Southamerika, they're the same, so it's fine, but just so you don't get a surprise like me. :)
Location couldn't be any better, just a couple blocks from all buses and metro, but I actually walked everywhere, it's as central as it gets!
Wifi works everywhere, incl rooms, they have a rooter per floor. Totally recommend it.