If I am not mistaken the 40mm and 50mm lenses would be prime lenses. If you don't need a zoom lens then either of those should be fine. The 40mm would be wider than the 50mm. This site - http://www.cameralabs.com/reviews/Canon_EF_40mm_f2-8_STM/ - compares a Canon 40mm lens to a Canon 50mm lens.
If I am not mistaken the 40mm and 50mm lenses would be prime lenses. If you don't need a zoom lens then either of those should be fine. The 40mm would be wider than the 50mm. This site - http://www.cameralabs.com/reviews/Canon_EF_40mm_f2-8_STM/ - compares a Canon 40mm lens to a Canon 50mm lens.