I'll be honest, I really hate them. Obviously they're easy enough if you write them yourself and/or know the code well, but I feel it impacts code legibility too much, plus I don't see any benefit from them.

Actually, what benefit do you see from them? Maybe I'm just not appreciating their brevity.

The reason so many people dislike this is because of versioning. Writing css with the single line method is really tough when working with teams or other developers.

via http://www.theparticlelab.com/single-line-vs-multi-line-css-plus-textmate-tips/

The single line is reserved for when you only have one css declaration, such as:

.code-block { background: #fff; } or .something-else { width: 100%; }

On 1 line, it's hard to read/edit them. At least for me.

Alphabetical order is certainly the easiest to make as policy, there's no room for misinterpretation.

However I prefer his model, as it puts related properties together such as for size, i.e., width, height, padding.

You say you prefer alphabetical order, yet your example is what Mark recommends. I think your example is the ideal as everyone should know the box-model. Padding should be on the same line as width and height, as it relates to size, not positioning like margin.

The downside of this method is that it's not as easy to make policy for. That isn't important if you are the sole maintainer, but if you have several team members modifying your CSS, guidelines are useful.

I tend to group CSS properties like you too, eg: top: 0; left: 0;. It makes sense to me.

I also don't like the idea of placing prefixed properties before everything. If anything, they should go last.

Not sure what you mean by that. They'd go last in my declarations if they were to do with styling, but the vendor prefixed property should always get declared before the non-prefixed property.

eg:

Prefixes are a hack, so we want to cascade to the standard property if it's available.

I've always preferred a tab size of 4 spaces, but I think it's largely just personal preference. With something like CSS, it gets minified anyway, so I'd rather be able to read it easily while I'm coding.

It's personal preference. I think a lot of the crew at GitHub are Ruby guys and Ruby is a 2-space language. The only thing that really matters is that the team you're working on is consistent because you'll give your version control repository a good working if everyone is doing something different.