all of them. They all offer different filters. I don't have 7 (wish that I did) but 5 and 6 are great. I think I use them in about all of my images. KPT5 can be used for fractals. KPT6 has lens flares, a scene builder, sky effects and a few filters called gel and goo. So, it depends on what you want to do really. I think 7 has lightning effects - I'm not sure though. There are a few here that have it. Maybe they can go on about 7 a bit more. Hope that helps. : )