I find that trying to compare ammo when shooting offhand is pretty close to worthless. I can't shoot the same size group twice in a row, even when using the same ammo.
I have benched various .22 ammo types, and even used a Ransom rest on occasion, and the results are interesting. Even the cheapest ammo will group within two inches at our 20 yard range in a good gun, like the Trophy mentioned above. Something less fancy, like a GSG, will maybe do three inches with budget ammo. Good ammo, and the CCI Standard can be included here, will group within a dime size at 20 yards when all goes well (maybe 1.5 inches in a GSG).
The hard part with ammo choice, is that you probably won't notice better scores until you're a better shot. If you imagine your 3 inch group ammo can be up to 1.5" off target, if you waver your sights around several inches when aiming, your group size may not be affected much. There's always a possibility that if you aim 1.5" to the left, and your budget ammo shoots (random chance) 1.5" right, you'll get a bullseye you didn't really deserve. If you aim 1.5" left, and the shot goes another 1.5" left, then things get worse.
But the closer you are to a consistent aim, the more you need better ammo to pay off.
The other big issue, when shooting bullseye on a timed line, are alibis - when your gun goes click instead of bang, and it not only ends up costing you points, but puts that bug in the back of your mind about your next shot going click when you should be concentrating on aim, trigger pull, and breathing. Cheaper bulk ammo is nearly always less reliable than the good stuff. It also doesn't ingratiate yourself with the other shooters who have to wait around for your alibi shoots, and have to score your alibi littered targets.