What is the best character to separate links? E.g: 1) <a></a> - <a></a> 2) <a></a> | <a></a> 3) <a></a> (other) <a></a>
I don't think it makes any difference at all. SEO is common sense. You will notice that most of the DigitalPoint members use "|" to separate the links in their signatures. I believe related text around the sig links would help more for SEO than different link separators. Try that
There would be absolutely no difference. It might be important gathering the links having the same themes and from the similar web niches but the way they have been separated on the web makes no difference.