"Stalvan"I know it's at the target. And I need to know what's the best range of all rifles mentioned above.
The answer to that is not easy. If I had to make some sweeping pronouncements about hunting small game (squirrels and rabbits) with an air rifle I would say:
The Brits shoot 12 fpe rifles much of the time and that seems to be enough power for a good marksman to take squirrels and rabbits out to about 40 yards but some of those fellows can keep all their shots on a dime at fifty meters (55 yards) and take the occasional magpie, rabbit, or squirrel that far out. I wouldn't consider such a shot myself but I am not able to keep all my shots on a dime at 50 meters with anything I own.
I would recommend rather a rifle in the 14 to 16 fpe range in .177 for hunting small game at ranges under 50 yards. I would also tamp down any expectation of making such shots as a new hunter. You will need to set up your rifle, select a pellet for it, and probably learn to estimate wind, range, and drop. You may need to practice your shooting skills. There are a lot of shooters out there who think they can shoot a 1" group at 50 yards under hunting conditions. The truth is that it is a lot harder than it sounds to shoot that well and if you can't do that you have no business taking shots at small game at that range.
From a purely practical perspective; I personally, am pleased to believe that using my 14 fpe Diana Model 36 (a modest spring rifle) with a 2 x 7 BSA optic I can humanely harvest squirrels with head shots out to 40 yards on a calm day
if I can find a solid rest. The gun itself is capable of a bit more than that but not more than about 50 yards with the pellets it likes.
So start slow, practice a lot, limit your shots to 35 yards or less in the beginning. You will do well.