I'll kick in for the Avenger as well. I have synthetic stock version and I like it's lightness a lot. I've watched videos about this rifle and folks say it isn't picky about ammo. That is not my experience, mine is very picky. But on the other hand, I shoot 50 to 100 meters the vast majority of the time and that's a whole lot different than shooting 25 yards or less.
Mine will not shoot slugs at all. Not one bit.
In any case, it's a great deal. Regulated, 4350psi, adjustable shot psi, adjustable hammer spring, adjustable trigger and a Weaver rail. It's hard to beat and you can easily do worse.
Both .177 and .22 are easily blown around by wind, but if you are familiar with ballistics at all, a higher ballistic coefficient is always better and the heavier 22's are better as you go further down range, in most cases. The cost difference is not huge between them until you get to the ultra heavy pellets.
The Avenger is new on the market and folks are just now starting to come up with modifications and after market parts are not yet really available. This is a real downside compared to a Gauntlet or Marauder. I feel pretty certain that this is going to rapidly change and mods will be coming in soon. I'm really hoping someone figures out how to put a FX STX barrel on an Avenger, but that is definitely another thread.