I've always heard PhotoShop's jpeg compression was very good. For the price though I could get CorelDraw and have enough left to buy a PC :-) Even that would be overkill since my old PhotoPaint 8 has more features than I'll ever use. From what I've seen the IBL in Poser 6 is very nice but I don't know if it can use .hdr format files for lightprobes. You can use PoseRay to export to POVRay and use .hdr image based lighting (.hdr converted to .pfm in HDRShop), so even Poser 4 users can use HDRI with a little effort.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken