I'd recommend my Smith 686, 6 inch barrel, if you want a pellet gun for serious Police/Practical comps.
Also, my Walther PPK, if you want a fun and very low cost plinker. It offers true autoloading pistol action - the slide works automatically, and you can feel the recoil - and it really is an auto pistol, NOT an autoloading design with a revolver mechanism. Loads 15 BB's (NOT pellets) from a magazine.
Jim