>>53117731Rated in regards to ambition, skill, knowledge, and power of the Pokemon they possess:
Iris >>> Misty > Brock > Clemont > Cilan > Dawn > Serena > May > Lillie
Iris is the clear winner because she's been shown to have powerful pokemon, is a regional champion, and is an expert on dragon pokemon. Misty is above Brock because she's more dedicated to battling specifically and determined to be the best, plus she's got some heavy hitters behind her. Her skill is high as well, given that she was able to keep up with a champion level opponent even in a friendly match.
Brock's above Clemont and Cilan because the pokemon we've seen him use are stronger than anything they have, and his knowledge of pokemon as a breeder/physician is probably the highest of everyone listed. Dawn, Serena, and May aren't weak battlers but battling isn't their main focus and their pokemon are trained to perform more than fight. Lillie probably has the least fighting experience of anyone listed period.