The most memorable would probably be Brock, Misty, or Cilan due to nostalgia (B/M) and/or the anime (Cilan in particular). Another strong candidate would be Elesa (particularly due to showy BW2 changes).
The least memorable would probably be Pryce (short of being a Special fan), Juan (no one really remembers him), or maybe Brawly.They were just sort of there for a lot of their games.
"Murder of the living is tragic, but murder of the idea is unforgivable." - Janus, speaker of the synod
Half the gym leaders from Johto. I can only remember Faulkner, Jasmine, Whitney, Pryce, and Claire. Most memorable is Brock, because I've faced him the most times out of any, and he has a huge role in the anime.
Everything in life is a battle. Even peace itself is a battle to maintain it.