If I had to choose one un-handled infill smoother, it would be the K6. I have medium sized hands, and prefer smaller, more nimble planes, so the K6 fits me perfectly. For someone with larger hands, the K7 might be a better fit. The K6 is slightly narrower than the K7 and the SNo.4.  If you have smaller hands or slender fingers, or a preference for small planes, this plane would be a really good fit. The scoop on the front pad is not functional in that your thumb or finger does not fit into it, but is a key aesthetic detail in the k-series of planes.