Rankwise: Meiling
Heightwise: Remilia

Pool asked:
Who has the lowest standing at the SDM?

I'd say Sakuya.

Poll: Who has the lowest standing at the SDM?

Going by the number of Danbooru posts:
Hong Meiling...16k
Patchouli Knowledge...20k
Izayoi Sakuya...28k
Remilia Scarlet...27k
Flandre Scarlet...23k

The real answer, however, is Koakuma, who doesn't even have enough standing to be included in the poll. Heck, she doesn't even have enough standing to get spellcards or an actual name...