On a budget, Avenger is hard to beat as a learning platform. So much is adjustable so easily that if you have anything remotely within you of the tinkerer or serious hobbyist, I don't know if you could find a cheaper PLUS easier way to begin to play with settings to learn what the hobby is all about. Even more so because Steve at AEAC and AEAC Volg on youtube has given three prescriptions for an economy, a regular, and a high power tune for that rifle in.22, plus ammo choice results. Ted's Holdover did some ammo and accuracy tests too. So you can play on your own, dial into any of Steve's settings immediately and see what happens, or take it further into your own experimentation with a path well laid-out before you.
As to quality? It's early. Time will tell. Many love it but not everyone will, or does.
.25's do take a lot more air -- and trips to the pump or tank -- to get your shooting time in. This reduces joy. Up to you.
There are enough videos out now of people liking and testing the Avenger out in .22 and .25 that you can be assured that either should be fine. So at this point it's what appeals to you and meets your needs.
I do want to mention, though, that pumping gets tiresome FAST. If only because it saps precious time from your fun-sessions. Or hunting opportunities, whatever. Even between .22 and .25, that can make a difference. And the Avenger's air cylinder is substantial.
Budget scopes? Look at them on Pyramid. Tons of them with tons of reviews. An old reliable are the UTG/Leapers "bug busters." You won't see many swearing by them here, but we have a lot of folks not into budget items here. There is nothing wrong with starting on a budget and only working your way up when and if and how you want to. Smartest option as often as not.