Though it's debatable, I've heard the majority of CSS developers prefer multi-line because of the ease of which a property can be found within the CSS file. But doesn't this make the CSS file bigger and less readable on the whole? I think single-line lets you scan the CSS file much faster. Any thoughts?
This is a matter of personal style - make sure whatever you choose that you are consistent. I personally tend to put each property on its own line for readability.
Use whatever style you find easy, at the time of development.
You can use a CSS minifier to reduce the size of the file at the time of deployment. You can find a lot of CSS minifiers which will help reducing the file size.
YUI compressor is a good one.
Just like JavaScript code, you would want to format your CSS the way that would conform to your team's standard, and let the compressor minifies it for deployment.
IMO multi-line CSS is better because its more readable. But i would suggest you to follow your teams's standard and dont waste your time debating :)
And if you are worried about CSS file size, then you should minify / compress it.
Also, if you have time, you spend some on validating your CSS using Official W3C CSS Test Suites.
It's all a matter of preference based on what your team decides on. However, here's my take on why I use single-line formatting:
When I need to maintain CSS, I'm most often looking to modify an existing selector. If the start of every line is a new selector, and not just more style declarations, it makes it easier to scan the document for the selector I want to find. It also means less scrolling to find what I need.
Once I've found the selector I need to edit, good syntax highlighting makes it easy to read the rules for a specific selector, so I don't lose any readability by having all of my style declarations on a single line.
That being said, I wouldn't say it helps with file size any. I rely on YUI Compressor to compress my CSS for me automatically, rather than trying to manually maintain an efficiently declared style document.