Which pellet

[rex]

Most modern pellets are fine at range
Stick to around 16 grains is my advice

[aris]

You can narrow it down by stating what rifle you have - and calibre, and people with the same rifle can tell you what they use. Then you can test those, and also in differing sizes. For instance many of the better pellet producers offer .177 In .450, .451, .452, .453

There are various sellers who will sell you tester packs of 10 or 20 of each kind of pellet you choose so you don't have to buy a whole tin of each.