When looking for the "golden" pellet I find that personal preferences don't mean much - it's what YOUR gun like that is important (5 guns off the assembly line might like different pellets) so you have to try different ones to find out what works best.
Through weighing and head-sizing I have seen a LOT of variation in cheap pellets so I recommend that for serious shooting that you use good quality pellets. Cheap "box store" pellets are fine for close range pinking but I wouldn't use them where accuracy is a concern.
I suggest that you clean the barrel and shoot a 500-1000 pellets to break in the rifle and get used to it so you can confidently shoot good groups. Get sampler packs of quality pellets for your testing.
For the actual testing, clean the barrel and "season" it with a dozen shots or so before each test. Do your testing in the best possible conditions, with no distractions and when you are relaxed and calm (go easy on the coffee LOL!). Shoot 5, 5 shot groups a 30 yards (shooting at closer range just makes one ragged hole that doesn't tell you much) taking a break between each group - I like to walk down to the target after every 5 shots. Don't try to test a dozen pellets in one session - take a break from testing if you start to lose your focus. Make notes on the target with all the pertinent details.
25 shots per pellet is a small sample size but is usually enough start eliminating pellets that the gun doesn't like, By repeating the tests you should end up with a pellet - or hopefully, several pellets that the gun shoots well.
Good luck and have fun!
BTW, most of my rifles shoot JSB pellets well.