Fastest billboard objects

I need to put halos around candles and such stuff using very simple billboards.

The first idea was to use the particles to make it, and I've done it already but I thought it could be expensive so I made a little search about it.

I found a couple interesting links:
http://www.41post.com/3770/programming/unity-creating-a-simple-billboard
http://answers.unity3d.com/questions/26770/prefab-billboard-with-a-transparency-texture.html

Now, the first link brings to a short tutorial on how to set up the particle system to make your billboard, while the second link brings to Unity Answers where they say it's better to just make a plane that always faces the camera.

I would like to know which method is absolutely the simplest and fastest to set up and less intensive for CPU and GPU as well.

Do any of you have any clue about this?
What method do you use?

 

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Also interested in this! Thanks for the links so far.

Our project uses procedurally generated 2-triangle meshes to reduce the amount of geometry (the built in Panel primitive uses 200), but in the profiler, they seem to take longer to draw than the built-in Primitives! Weird.