If you're asking about web design software, then I would say Photoshop all the way.

But for other purposes, I use Photoshop, Paint Shop Pro, CorelDraw, Flash.

ok, for those who don't know the difference between bitmap (raster) and vector graphics, here is the explanation:

Bitmaps or raster images are dependent on resolution. They are formed pixel by pixel. Hence given any bitmap image, if you try to enlarge it, it will appear distorted since it is resolution-dependent.

On the other hand, vector graphics are formed by lines and curves determined by mathematical functions......hence, when you draw an image in a vector software like Illustrator, CorelDraw or Flash, it is entirely formed of lines and curves.
Vectors are independent of resolution, hence if you scale their size, they will retain the original quality with hardly any loss (because everytime, the image is recalculated mathematically)
This is particularly useful when you are creating some image where you don't know what the final output size would be.