Which symbol to use for polarized capacitor?
All of these are listed in assorted "standards", and so are correct. But different symbols are more prevalent depending on your geographical location.  

The American standard is IEEE 315 and the European is IEC 60617.  There is enough crossover, however, that people are accustomed to seeing both types of symbols.

In the USA, I almost always see



for non-polarized caps, and



with or without the plus sign for polarized caps. That is, the curve generally denotes polarization.  I seldom (almost never) see the curved line used for non-polarized caps.

These IEEE symbols are also common on non-USA schematics.  On sheets with  European-style symbols, I usually only see these:



Sometimes the + side of the polarized cap has a white box, but black or white, the + sign always seems to be there.

As people are saying in the comments, choose either:


Whatever you like, or
Whatever your company (or customer) likes.