I use amazon the most. I also manually enter a lot of things like comics and zines (still have a stack to read and enter!) I use amazon because they usually have what I want and I manually enter because the zines/comics don't have isbns.
Here's the breakdown:
|Library of Congress
Not sure why there are two amazon's and two manual entries. Does anyone else's show up like that? I think the amazon uk is for some of the books I bought while in England. Not sure what I used the Library of Congress for.
What's your breakdown look like? You can find it at your Librarything Profile and then under Statistics.