I used to always use Manual, it must be because I was brought up with old SLR technology where you took the lightmeter reading of the camera as a general guide. Usually I would look in the viewfinder and decide on the spot whether I should over expose a bit or under expose a bit depending on how much contrast difference there is in the picture. DSLR cameras today are dramatically betterthough, and you really can get accurate spot readings, and choose both your focus and lightmeter point very accurately ... plus you can get immediate feedback as soon as you take the picture because the picture develops instantly
To be honest though, using Av or Tv can also be considered to be close to Manual. I mean in low light you are most likely to use the widest lens aperture anyway so might as well leave it there and let the camera decide on shutter speed. Of course you can add or reduce the exposure ... so really Av or Tv is simply an advanced Manual mode. As for the other settings on the dial, I really never even bother to look at, except for a video mode if it exists. But I do know that my wife swears by the "Green Box Mode" and gets some pretty decent results.