Only advice I have, is don't let the recommendation of the older "holy grail" rifles from dudes looking through rose colored glasses lead you to spend a lot of money on something that's no longer in production. I've had most all of them, and for the most part, there's a good reason they were discontinued.
If you want my opinion of the best springer you could ever buy, here it is:
HW77K or an HW97K in .177 running at 12fpe with a drop in ARH tune kit.
No, they won't group in a dime at 75 yards consistently. Yes, they are heavy. Yes, they have twang out of the box. No, they won't shoot 17fpe and still be able to hit anything.
But they don't have lockup issues like the "other" famous underlever. They are readily available new. They aren't as heavy or complicated as the RWS54 or 56. They are easier to shoot accurately than the break barrels. They have excellent triggers.
I've had about all of them at one time or another and those are what I can recommend to be consistently good performers. The current production has quite a bit of spring preload, and really need turned down a bit to be their best IMO. A simple drop in tune kit from ARH will be all they need to remedy that.
Good luck and have fun.