They can all be decent guidelines. In general, ignoring the focal length doesn't make a lot of sense though since it is always going to magnify shake. A lot of other factors come in to play though and these are just rules of thumb. If you have any kind of image stabilization it will throw these off.

Also, some people are much more steady than others. Personally, I'm a trained marksman and the same support and breathing techniques that I use for shooting a gun can be adapted to shooting with a camera, so for me, I can shoot much slower shots than most people without a tripod. If you're new to photography and don't have very steady hands, then your maximum exposure time is probably going to be much lower.

Your best bet is to try it for yourself and see what results you get. No equation is going to make a substitute for experience and knowledge of how well you can hold a camera still.