Others have already given you the winning formula for an HK in USPSA. VP9 with Dawson sights and a lot of practice. Trigger preference is up to you and how sensitive you are to it. My competition VP9 currently has an ultra-match spring kit from HKParts, a slight polish by me, and a super secret squirrel prototype striker assembly from an HK guru at HK Zentrale. Before all that, I did just fine with the trigger stock, but the lighter trigger does make it easier to pay less attention on 20yard mini-poppers and still get good hits.
I moved from a Mink tuned CZ75 SP01 to the VP9, it's not a handicap. I love that I really don't have to worry if my pistol will run or not, it just works. Oh, and hits exactly where I aim.