For best results, there should be no EVs on the Pokémon. You need a range of levels for the best IV determination. I recommend (if hatched) Lv1 and Lv100, which is what I use. If caught, whatever level you caught it at and Lv100. You need to do a WFC Battle to check @Lv100.
Thank you very much
Another question Out of the Elite 4, Lance, Red, and gym leader rematches, which of their pokemon have held items and which items are they?