Though I can often be found reading from a stack of magazines in an uncomfortable corner at the nearest Chapters, Nicholas Hoare is a haven to read a good book.
The atmosphere is great- the gorgeous brick wall, the friendly staff and the people who frequent it, are all unmatched.
The sheer size of it does however limit its ability to carry as many books as it's Walmart-like competitors. But if you're looking to find a good book and read all day, this is definitely a good match for you.