I've seen 3 GSG's at Appleseeds so far.
None of them has even lasted the weekend, let alone produced groups that earn the Rifleman distinction. It is not a very precise long gun, IMO. I've put either a 10/22 or Marlin 795 into the hands of one of those shooters and his group size cut in half. Immediately.
Sig P229 is a handgun, not a rifle.
Not impressed with the reliability of the AR .22 conversions out there, either.
Frankly, nothing beats the sturdiness and time tested designs of the Marlin 795, Ruger 10/22, Remington 597 and others of the traditional autoloading rimfire rifle genre. They work. Plain and simple.
$$$'s to donuts, my money is on a Marlin 795 with TechSights as the best "appleseed" rifle. I use two of them as loaners when a shooter's primary rifle goes down and he doesn't have a spare.
The line safety officers will thank you for it, over a 10/22, also. Those flush Ruger mags start to become invisible as the day drags on and you've cleared the line for the eleventy-first time. The Marlin, being a stick mag, is harder to miss.
But, bring the 10/22 you have. Appleseed is about YOUR gear. Not a gear race. Scopes are welcome, click-adjustable sights are welcome. Any sight that is scientifically adjustable is welcome.
(And, we'll even put up with the "whack it sideways" stock sights on Ruger 10/22's if that's all ya got.
You'll just miss out on the pleasant part of sighting in with scientifically adjustable sights, and be relegated to the guess-n-check methodology.)