The best sex positions are those sex positions that deliver the most sexual satisfaction.
The best sex position from the men's perspective is, for example, a doggy style or reverse cowgirl; aside from physical stimulation, these positions also provide visual stimulation, which is very sexually stimulating for men (see the images above).
The best sex position for a woman is, for example, the missionary sex position (see above), with face-to-face contact, avoking closeness and intimacy while offering physical stimulation of the vagina and clitoris.
Placing a pillow under to elevate the woman's pelvis intensifies her sexual pleasure due to an increased blood flow and the man's ability to thrust his penis into the vagina from a variety of angles.