Textfield properties - differences in Anti-alias

Anti-aliasing, basically, removes 'jaggies' and 'pixelation' by smoothing out vectors. So on things like text, which are vectors, the text looks smooth.

Device fonts uses the fonts of the users operating system and are not anti-aliased. So they will appear jagged and pixely. However people can take advantage of making sure characters (especially asian multi-byte) are available and do not need to be embedded into flash saving you lots of file size.

Anti-alias for animation is a less expensive, easier to render but softer looking version of anti-aliasing. Good for non-text vectors. They call it animation because it's easier on the processor to render.

Anti-alias for readability adds a contrast bump to edges making text look sharper, thus more readable.

The bitmap-text isn't vector. It saves the text as bitmaps and typically you'd only do this if you intend to use bitmaps. You choose the size of the font and then it's not really good to use alternate sizes for fonts other than what you select. This is useful for games who sometimes don't want the overhead of rendering the vectors for text. Instead the text is just a bitmap and is easier to render.