Is it better to store images in a BLOB or just the URL?
As you can tell from the other answers, this is a big "It Depends." Some other factors might be if you are paying for hosting, do they charge more for file storage or database storage. File storage is typically cheaper, especially for cloud services.

If you are self hosted and using SQL Server, the upcoming version, codename Denali, will extend FILESTREAM to allow access via both TSQL and file system. It also will make sure these stay in sync. You can access, update, delete from either side and it will keep everything organized.

Do your research and find out what's important to you and pick the direction based on that choice.