I've stayed in both multiple times. With Platino, it depends which room you get. Some rooms are really very, very small even for an overnight stay. That was the case for our last stay a few years back. They said the bed was a queen size but honestly it was full size on that particular room. Bathrooms are also very small. Breakfast wasn't included but they do have a restaurant where you can grab something to eat. I can't remember how good the wi fi was.
Since then, we stayed at Matum. Rooms are good size, bathrooms need some work. Wi fi is pretty bad within the rooms. It works well in the second floor hall, in front of the restaurant. Breakfast buffet included but not very good. For me, it was just a toast and coffee.
Our last trip we ended up in Centro de Santiago, a B&B/Guesthouse with nice rooms, which we found in booking.com We liked it and is cheaper than both Matum and Platino. Wi fi was just fine. I don't recall that it had breakfast included. It's been a few months ;-)
Between Matum and Platino I think I'll stick to Platino, but as long as we're driving, Centro de Santiago is much better.