I prefer Illustrator to Photoshop for composing graphics. Because Illustrator is specialized on vector graphics, most of the editing is non-destructive: e.g. you can apply a blur effect to a layer, then modify the original graphics in that layer and the blurring is re-applied. You can also change the parameters of an effect at anytime. Illustrator gives you much more freedom. The only thing you can't do is work with individual pixels. But I found that I never needed that feature in Illustrator. Besides, working with pixels is tedious and erratic.