Use the term "best" with caution... usually the "best" isn't cheap.
For portraiture, where a blurred background is often preferred to help separate a tack-sharp subject from the background, a "full frame" sensor camera is able to generate more blur. Your camera has an APS-C size sensor so things change a bit.
For food photography I typically always use a macro lens. On your camera I'd use the EF-S 60mm f/2.8 Macro USM. I use the EF 100mm f/2.8L IS USM but I"m on a full-frame camera. One reason that I use a Macro is because when I'm shooting food I'll often be including detail shots and for that I need the close-focusing distance. Also Macro lenses tend to have optics designed to offer very good detail resolving capability (the "MTF" curve that shows off the accutance of the lens is usually much higher than a lens that you'd use for portraits. In fact... for portraits you sometimes deliberately want to "smooth" the subject's skin, etc... too much detail often doesn't look as attractive.)
For portraiture it really depends on if you're shooting indoors vs. outdoors ("studio" vs. "environmental" portraiture). A longer lens tends to work really well, but you have to be much farther from your subject and indoors you typically don't have the space.
When shooting (especially indoors) there's the notion of the portrait size... is it a "head & shoulders" shot, a "half-shot" (shooting the subject from the waist up), or a "three-quarters" shot ... or a "full shot" (entire body from head to toe). The 85mm is a nice focal length for portaits outdoors, but indoors an 85mm lens will limit you to "half shots" (usually just a single subject in the frame and you can capture them from waist-up) because getting multiple subjects or full-length shots will require a much larger room so you can move back farther. Using an 85mm lens on an APS-C crop-frame body is roughly the same as using a 135mm on a full-frame body in terms of the true angle of view.
A 50mm will buy you more angle of view but you wont be able to produce quite as much blur. The new 50mm f/1.8 'STM' (emphasis on it needing to be the STM) moved up to 7 aperture blades from the previous f/1.8 non-STM which only had 5 blades (and they weren't well-rounded). The quality of blur is noticeable smoother on the STM version of the lens.
BTW, when I shoot food, I seldom use a focal ratio lower than f/4... I typically at least want the main dish to be focused even if I want everything else blurred and when I do want everything else blurred I typically want the items to be blurred... but at least recognizable to the point that they offer the suggestion of what they are (e.g. I want the viewer to notice there's a "wine bottle" in the background even if they can't actually read the label.).
Tim Campbell
5D III, 5D IV, 60Da
