Most recommended film among the following is:
The types of film used most often in the United States are Ultra-speed (group D) and INSIGHT (high end of the E speed range with manual processing and F with automatic processing conditions). INSIGHT film is preferred because it requires approximately half the exposure time and thus half the radiation dose of Ultra-speed film. 
Multiple studies have found that E/F-speed film is preferred because it has the same useful density range, latitude, contrast, and image quality as D-speed films and can be used in routine intraoral radiographic examinations without sacrifice of diagnostic information.
The current F speed film require about 75% less exposure of E speed film and only 40% of D speed film.
White and Pharoah's Oral  Radiology Principles and Interpretation 8th edition
C film
E film
D film
U film