Fonts

Why do some fonts look crisp and others blurry?
I have followed the “rules” for getting a crisp font (using the correct size - even numbers and the size for which the font was intended and ensuring an integer x and y position), but I was wondering if there are any particular fonts that you have found to work particularly well when presenting text information.
I have downloaded a couple from Flashkit; can anyone recommend any good fonts?

Also, I’m not sure what the Alias feature in MX actually does and how one should use it.

Any input is much appreciated.