Bob:
Yours is a great question, albeit one that really isn't easy to answer, in the sense that compared to my firearms experience, which has been devoid of grief, my airgun experience has not. The only airguns I've owned which I would deem to be fully satisfactory out of the box are my pair of R-9's, one of the five M-2004 pistols that I've purchased, and a P-1 pistol. I've had issues with virtually everything else.
It all started years ago with premature mainspring failure in a .177 Webley Omega. That was followed with a .20 R-1 that was a dissappointment in the accuracy department compared to similar rifles of the same model and caliber owned by friends and associates. More recently, I had problems with a Benjamin Legacy wherein the barrel ceased to lock up properly. Instead of fixing it, Crosman sent me another. This one fried the piston seal in short order and had other issues. That got sent back and replaced with a 397 Benji that I put 20 rounds through before the valve whent kaput. Moving on, a pair of Gamo Shadows proved inaccurate and downright rudely mannered initially, though they did smooth out nicely to become respectable shooters. I gave mine away. My wife still has hers and throughly enjoys it. Out of the box, however, both were pretty poor shooters.
I jumped on the" M-2004 pistols from Wal-Mart" craze and the first one wouldn't fire. I went through 5 of them before finding one that works. This was perhaps the biggest dissappointment -that a company could put out five of something that didn't work for every one of the same something that did.
The lone M-2004 that worked well shot great out of the box and still shoots great with several thousand rounds through it. It is one of my favorite airguns and is very accurate.
The R-9's, likewise, were accurate out of the box and left nothing to complain about.
Both of the R-1's I've owned have had little problems that needed to be fixed under warranty.
I guess the point is that after over two decades of airgunning, I am more surprised when an airgun actually functions properly out of the box than I am when it doesn't. I pick the M-2004 as worst because so many of them I bought didn't work. But the one that does work is something I wouldn't want to part with.
Like I said, it's a tough question to answer..........
-JP