We have been asked this question before and it really depends on the situation and use case.

1. In depends on many factors.
2. Base64 encoding enlarges file sizes by up to 33%
3. If quality is your focus, I recommend URL/URIs.

I would love to hear more about this project and provide some more insight. Let me know if you have any other questions.

-Steve

Speed: depends on multiple factors like connectivity

Size: base64 takes up much more space

Image Clarity: files will give you more flexibility over quality and file size.

I recommend files.

I think that image file URLs are best and this is why:

* Base64 Strings and Files might have the same quality if your string is a encoded version of your image file
* Base64 Strings are much bigger than binary files (Usually 33% bigger) - http://davidbcalhoun.com/2011/when-to-base64-encode-images-and-when-not-to
* You only need Base64 when delivering the image using channels that are 7-bit encoded like emails, text files, CSS, HTML or other medium that only allows lower ascii characters.
* Gzipped images have the shortest size and pure binary image files are the faster to decode/display