I'd say most memorable is Brock, and most forgettable is Candice. Interestingly, for me, all of the Ice-type leaders qualified as the most forgettable leaders in their respective regions. If I had to pick a region with the most forgettable leaders, it would be Sinnoh; I might be able to name them all now, but I probably wouldn't have been able to a few minutes ago before I looked them all up.
"Why don't you just take this picture for what it is? Teemo being stuffed and mounted by renek." - Serenderpity LoL Name: Thanamar
Most memorable- All of the Kanto Gym Leaders: Brock, Misty, Lt. Surge, Erica, Sabrina, Koga, Blaine, and Giovanni (I can remember their name and type from the back of my head and I even played Pokemon R/B. How can I not remember them)
I love and believe in Jesus Christ and are 100% proud of it Iris's Official Future Husband.
Most forgetable: People are gonna hate me for this, but Koga. Since I started the games on GSC then went backward, Janine hits my mind before him... Gym Leader wise. I don't forget any Leaders, Champs, or Elite Four, but I sometimes forget that Koga was promoted... so semantics here.
Most Memorable: Several, but especially Morty for being the biggest hurdle in my childhood.
Official Spike of the PSASBR Board Fan of a "pretty hardcore evil" Vampire Queen.