Arian, The best ammo to use is whatever shoots best in your gun. The only way to determine that is to try out a bunch of different pellets and see what groups best.
As for power, wadcutters tend to lose energy very fast and are OK at short range but not much good at longer ranges. Diabolo (round nose) pellets tend to retain energy better than wadcutters or pointed pellets. These are usually the best from longer range shots.
Also, if you gun has enough power you can try some heavier pellets like the crosman premier heavy or JSB exact heavy. These will shoot slower but carry a bigger thump downrange.
If you are having accuracy problems make sure the scope is mounted tightly to the gun. On springers you often need a scope stop or a one piece mount. As the reverse recoil from the spring can cause the mount to "creep." Also, springers require an airgun scope. As the spring recoil can loosen the optics in a standard scope.
If the scope is fine, make sure the action is tight in the stock. If its a breakbarrel check to see that the barrel lockup is tight.
Some cheaper guns need a bit of work before they shoot well. Sometimes its just a matter of picking the right pellets.
