The Marriott is one of the nicest hotels in Quito. I have stayed there AND at Cuba Vieja (also a GREAT place) and I would not worry about leaving my laptop at either place. They both have safes. I’m not sure they’re large enough for a laptop, but they are also very secure hotels. If you’re worried about it, ask the staff to put it in safekeeping for you. Personally, I wouldn’t worry about it, but I’d tuck it out of site in my luggage when I was gone. (The cleaning staff will leave the room door open when they clean — they don’t want to be accused of pilfering anything and I would not be concerned that they would.)