Keep in mind that it is a CROP factor, not a zoom factor. I find that a 50mm sees my subject as my eyes see the subject, though, of course, that which surrounds the subject will be cropped out of the final image. To get the same field of view with a 50mm on a crqopped frame, to include the environment surrounding the central subject, I need to move further back.
I have cropped-frame Canons, and three 50mm lenses, each with it's own personality and ideal uses. I am feeling the desire for a fast 35mm prime lens now, but I believe 50mm will remain my favored focal length.
I have tested the concept my walking around with a zoom set at 35mm. I do have 24/2.8 and 28/2.8 primes, which I find a bit wide much of the time, if I leave the house with either as an only lens. (I have nothing against wide lenses; indeed, my favorite zoom is the 10-22mm EF-S.)
This is just my way of seeing things. I am not an expert, just a serious beginner.
Also, I seem to remember a recent thread that polled members of the Cameralabs forum, regarding their pick as an only lens. A large portion of responses from pros seemed to be the 85mm, for a one-and-only lens. 85mm on a full-frame is fairly equivalent to a 50mm on a cropped-frame.
Canon 7D2/7D/5D/40D/1D2N/M3; Nikon F6/D700/FM3A/1Dx/Coolpix A; Canon 40mm 2.8 STM, 135L, 50L, 35L, 50mm 1.8 I, 100mm 2.8L Macro, 10-22mm EF-S, 400mm 5.6L; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S, 18mm 2.8D, 45mm 2.8 AI-P, 14-24mm 2.8G, 24-70mm 2.8G, Micro-Nikkor 60/2.8G; Voigtlander 90mm f/3.5 SL II