KeyShot can do some really amazing things as far as product renderings. You can turn simple 3D models into realistic images in a very short amount of time. I wish there were a way to manipulate the geometry once imported into KeyShot. The software allows this user to move geometry but not change its shape or form.
If you have high resolution images, it does a remarkably good job at resizing and resampling. It has to have something to work with, so I recommend it only be used on good quality images. On four to five megapixel images, I don't think it works as well as on my 20+ megapixel photos.
Keyshot has a simple and intuitive interface that makes it easy to use for quick renderings.
Through Keyshot's viewport, you can see real-time changes when replacing or adding textures to a 3D model.
The new Keyshot 8 comes with volumetric features such as fog that can add depth to your image making process without having to manually do it later in another program.
Honestly, I've only needed customer support a couple of times. One time was a question about licensing which their customer service explained very well and offered just the help I was looking for
Topaz always responds to my questions in a few hours or a day at most. They've been able to explain their answers and give detail I needed to complete my work. Their instructions are quite clear and easy to use. I haven't had to reference any third-party support sources to get answers.
Keyshot is simpler and more intuitive compared to Octane. That being said, Octane is far less expensive and can take advantage of a GPU making it more versatile.
Since they aren't direct competitors I don't expect PaintShop to hold up to a specialized piece of software. PaintShop allows you to resize but it's not intended to resample as well as Gigapixel AI.