Originally posted by SpecialK A prime is not a walk-around lens, unless you don't mean a single lens that covers most of the focal length range required to capture the majority of the images you will encounter on an unplanned casual outing :-)
70 is a good portrait length and short telephoto, however.
If I'm doing street photography, I want a prime; a zoom is too large and heavy and too slow to use in comparison to a prime. On the other hand, if I'm wandering around photographing buildings and store fronts, a zoom is the best lens. The 70, I find, is best for across-the-street street photography in terms of this discussion.