I use each one for it's best uses. As an example, I find Photoshop has more and easier-to-select options. The Polygonal Lasso tool is also highly useful for GT4-photoshopping. However, Paintshop Pro makes the process easier, and has MUCH better blur-tools - the Radial Blur, as an example, ends up much smoother, preserves more color, and has that option to make a spinning blur. However, I find that the selection-tools are pretty basic in PSP(7), and that the use of layers isn't fluid enough. I also don't like the results that "One-step Photo-fix" gives on GT4-shots. This tool is calibrated for real photography, and actually gives good results there. But on GT4, it makes the pictures look washed-out, and makes edges very.. umm... edgy. Try to take a fast-shutter shot in GT4 that includes trees (Trial Mountain would do), and apply the OSPF. I did it today, and the results weren't very nice.
Plus, for deleting the GT4 signature, nothing works as good the Photoshop tool "Patching". Simply select the area you want to delete (with the signature), look for a similar spot, and voila, a clean "real" photo...