Nogi and Chuuya are my favorite artists in this series.
Nogi even draws /e/ and /h/ material of the series from time to time. And is the only artist on the franchise who has actually released a doujin parody of the series they later got employment for officially. Quite a promotion.
Fuyukawa is nice too, and has started to draw the girls with thicker thighs lately. Fuyu was also an h artist but has since abandoned it. (Syouji)
Haimura's art is my least favorite in terms of girl design though. I don't like the weird legs he draws.
The anime character designer, Tanaka Yuuichi, also draws lewds of Railgun girls unofficially.
Arata? We don't talk about Arata.