I was thinking about this after shooting Sunday afternoon. I ran a few mags through a 9mm AR carbine I put together at Christmas time. What a hoot that thing is.
You should completely shoot that 9mm carbine in Pistol-Caliber Carbine division (either Open or Irons) at the upcoming Great Plains Steel Challenge Championship.
I just got a 9mm carbine recently also, and that thing is seriously fun to shoot. Primary Arms red dot, and a $30 muzzle brake on the end, and it is ridiculously easy to hit steel. Too much fun! Mine would be in Open division, obviously. If you don't have a muzzle break or comp, and just iron sights, Irons division would work for you...ahem.
https://easternnebraskapracticalshooters.com/2016-great-plains-steel-challenge-championship/ As for favorite gun to shoot---that's really hard to say.
I will say that I ALWAYS have fun when I'm shooting my Mark II Ruger 22/45 pistol. (4" bull barrel, fiber optic front sight, Volquartsen hammer/sear combo in it.)
But....I love shooting my G34 or G17 in USPSA or IDPA, I like shooting my new 10/22 Takedown (which I've modified A LOT), I enjoy my .223 and .308 ARs....
....it is really hard to pick just one!
I suppose that is a good thing, really.