My current most used primes are the 35mm 2.8 Macro Limited and the 70mm 2.4 Limited. Both green-ring versions. The 35 because I find that focal length really versatile on a crop sensor (pentax KP), it's a very sharp lens with great contrast, and the macro function makes it even more flexible. The 70 because it's the perfect small but long lens to take pictures of my kids and family without feeling obtrusive.
In particular, I really think people sleep on the 70. It's such a fantastic and unique lens, and I really like the pleasingly neutral and flexible way it renders images. And when have you ever seen a lens that long in focal length but tiny in size? It's wonderful.
I also use the 15 Limited but I don't think I need to add to that particular fanclub.
Here's two very different examples of the different shots you can get with the 35mm:
And here's a shot with the 70. This shot demonstrates one of the things I really like about the 70mm: calm, smooth bokeh that doesn't call attention to itself.