I have about 4500 fonts and I usually find it hard to find the one I want, I usually sift through about 100 before I find the font I want. I rarely use Serif fonts in artistic pieces, in fact, I rarely use Serif fonts at all. I just find Sans Serif fonts more smooth and "aesthetically pleasing". So I guess it's no surprise that I really don't think the font used for posts on this forum work well at all.
Out of all the default fonts, Verdana is my favourite, especially at around 9pt-13pt size. As for titles and things, Myriad Pro is always reliable. A less used but decent "banner/logo" font for games and the like is Microgramma, definitely one of my favourite less classical fonts.
As for signatures, I don't like using large text, if any text at all. If text needs to be seen to make the image what it is, I'll try and differ it more in terms of notability whilst retaining a consistent style in the piece. I don't like differing text styles from the art just to make it stand out. I also tend to keep text a low size in sigs. I haven't actually made any sigs for a long long time but maybe I'll make a few more when there are some new decent Legion renders out ^_^
