Personally, I disagree with the anti-aliasing idea if you want to produce professinal looking, transparent GIF images.
I find that setting the colour range at 256, and then the dithering method to 'None' produces the most satisfying results. This is especially true if you're producing low-resolution images, but want to keep as much detail as possible in the picture - using a dither of some sort tends to "muddy" the image, and the smaller the image, the greater the loss of sharpness when dithering (same as using any other image file format).
But rule of thumb is experiment; make good use of the multiple preview displays in programs like ImageReady to see how different settings produce different results.
- R34LiSM