Been thinking about this one… I have a few pistols, currently enjoying the gk1 no end. My knee-jerk answer is that the GK1 is of course the finest airgun i have handled.
But i also have a talon p, hatsan mod25 supercharger, webley tempest and one of those super cheap p17ssp guns.
Which pistol is my favorite? A tie between gk1 and the talon P if we can count the talon P as a pistol... That was the first pcp for me and that thing was the IDEAL starting platform- what a (good!) can of worms the airforce platform has been. I don't care how sweet the gk1 is at the moment, in light of my last 4 years of shooting and getting into the hobby, nothing can top the talon P. Totally rugged simple completely functional erector set type airgun, so easy to get parts, in-line tank and practically a direct tank-to-barrel setup with everything completely accessible. Beautiful utility airgun with minimalist / utilitarian design. Mine is currently decked out with an 18 inch barrel and a large tank and Condor valve but I'm tempted to restore it to its compact form one of these days.