I've been using Amigas for graphics since 1993 and by far my all time favorite is Deluxe Paint. To get the absolute full benefit of it you need the last version--5.2. 5.1 has a bug in the airbrush that is annoying. Image FX, Toaster Paint, TV Paint and Photogenics are also favorites of mine. Lately, I've been using Imagemaster RT which is a bit less intuitive but has a lot of hidden power.
Back in the day, I used Digi Paint and Photon Paint a lot and Imagine 2.0 for 3d stuff but now I use 3d Studio Max--a really old version--which is so much easier to use for the little bit of 3d graphics I do.
Part of the charm of the Amiga is not what they are cabable of but how they work with and influence my creative flow. Pcs and, to a lesser extent, Macs, tend to distract me more. My Amigas are dedicated to art and graphics 100% and I don't use them for anything else like writing or web browsing. Amigas make me think about things in a different way. I like the buffer architecture of a lot of Amiga graphics programs. It can be a difficult to work with at first but once you understand it, you can do incredible things with it. And then there's the classic Amiga trick of just being able to select part of an image and instantly turn it into a paint brush. I've never seen that on any other platform.
Here are examples of what I've done with Deluxe Paint. This was done with Deluxe Paint 5.2 and Imagemaster on my A4000.

This was done with Deluxe Paint in Winuae.

This is the same image processed with a Photoshop filter--I can't rember which one.
