Manda (マンダ)
The concept of Manda is cool, and there's no other monster in the Toho line-up like him, but to successfully pull off a snake-like dragon is obviously a difficult task, which perhaps explains his lacklustre appearances.
Rodan (ラドン Radon)
I've got quite the soft spot for Rodan. Invasion of the Astro Monster the first Godzilla sequel I ever watched and helped spawn my obsession with kaijū cinema.
Gorosaurus (ゴロザウルス Gorozaurusu)
Gorosaurus ranks highly on many fan lists of monster favourites, including my own. Perhaps it is his no-frills design and sympathetic aura that give him his edge.
Godzilla: Shōwa and Heisei eras
Wherever your preference lies - Shōwa, Heisei or Millennium - Godzilla fans should thank the great kaijū gods in the sky that we've been blessed with such an outrageous amount of excellent films!