In the Great League and the Ultra League the maximal CP of a Pokemon are capped at 1500 and 2500. Furthermore the IVs of a Pokemon matter in the CP calculation.
As I do not know the CP calculation I try to use Pokemon with good IVs in the PvP fights. Therefore I prefer Pokemon which have a 13+ Attack IV, 13+ Defense IV and 13+ HP IV.
But is this really the best option?
I found the following site which seems to suggest that a 1/15/15 Alolan Raichu is better in PvP than a 15/15/15 Alolan Raichu. But I can not find an explanation why this is the case.
And the most important part, does it matter in an actual battle?
I have seen that there are similar questions (this one Do individual values (IVs) really matter at lower levels? or this one What is better to have? A pokemon with higher IV but lower CP or vice versa?) but they do not consider PvP at all.