Gas or spring for forever gun.

if its a long lasting air gun you want Definitely go with a spring they last forever and if something does break its generally easier and cheaper to fix as to witch brand well that's a much harder choice and you'll have the same difficulty choosing a caliber i also recommend a wood stock a standard stock not a thumb hole because it's less likely to break and you can always redo the finish on the wood.
 
"Jonnes"
"scrane"Start forever a little earlier for her.
HW30.
I couldn't agree more, the HW30S is easy to cock for kids and will last you a life time. My son (at age 6) started out with one and now (5 years later) he still enjoys the heck out of it (and so does his dad by the way). Honestly, you can't go wrong with one of those. A friend of mine has a HW35 that belonged to his grandfather, the damn thing is at least 50 years old and still has the original spring. He recently replaced the piston seal, that's it. 
Those HW97's or TX200's are too heavy, in weight and cocking effort. Not a good rifle to start with for kids.
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I wholeheaRTEDLY AGREE WITH JONNES!
HW30 for young people, HW35 for older ones..
Tony Wall says the short shot cycle and stock design make the HW35E particularly well-suited to offhand.

Re. Spring longevity: I had to re-build my 1906 BSA due to the leather piston crumbling.
Dual opposed springs were slightly kinked but still doing their job. (Since I had the gun appart I replaced them with Vortek...Got me our Thanksgiving turkey with it! ;-)

Go quality springs with a spring compressor and spare spring & piston head if you are going to still be around in another 40 or 50 years & pickup box full of pellets down-range ;-)
Davo
 
Thanks guys I appreciate the advice. Just took her out shooting and it looks like she lacks the strength even for the hw30. Ive been giving her a bean bag to rest my mrodair precision mk2 pistol on and she did great. At 5 years old she was hitting a pie plate at 15 meters almost every time but baby steps right? Anyway ive been looking into some smaller kid sized co2s after seeing her struggle. When she turns 10 ill drop a couple racks to get her in to field target. Anyway I got the knowledge I needed and it turned out shes just not ready yet for a springer thanks again. 
 
Thoughts on a "forever rifle" that is a break barrel.

There are a few things I don't intend to go back to. A real springer is first on the list, but I am a hunter who spends time in the woods. Being able to load the NP and leave it loaded out weighs all the arguments for springs I have ever heard. At least for my purpose. A replacement ram is actually cheaper than a comparable power/smooth shooting spring kit.

Second on the list is any break barrel that doesn't have a picatinny type scope rail. Someone laughed about their scope moving every time they fired a shot in one of the threads a few days back, and I remember trying to keep a scope on a heavy springer when they just came with a couple of slots milled in the receiver to mount a scope. I had the scope literally fly off one of the B models back in the time period when James was still around. I have a friend that has a Gamo 220 type rifle and is fighting the springer scope mount wars right now. I need to order him a mount and stop piece as a gift. Of course, the mount, stop piece and a scope that will stand up to the recoil will cost more than he paid for the rifle.

I bought a beautiful Mendosa rifle that had a trigger you literally learned to pull with both fingers. Good power, decent accuracy, but even on a bench using lead shot bags, you could not shoot it consistently with that trigger. If it doesn't have a decent adjustable trigger, or there isn't an economical replacement, it isn't really even considered. I would really like a set trigger.

I am not brand loyal. CNC doesn't care what continent you plug it in on. My thoughts are strictly on shooting and using the item. My Trail is heavy, but I can load it and carry it on a five day trek knowing it will hit what I aim it at four days after I loaded it cold, on the first shot. The scope is still where I put it when I bought the gun unless I deliberately changed it. The trigger is a little over 1 pound, repeatable, and it breaks clean.

Not a commercial for the Trail, just the requirements for a "forever rifle" I would keep. Pretty or name brand/origin are not figured in. For me, it has to travel well, put up with living out of a tent in whatever weather for days, be loaded until needed, even if that if that is all week, and be shootable.