The answer is, of course, one from a page or site which is relevant to the search term you're trying to rank for.
Those of us who build WordPress-based websites have a huge amount of time for a guy from the Netherlands called Joost de Valk, whose most recent achievement is the stunning WordPress SEO plugin which I use on our website. But Joost also writes a good blog, called Yoast, and has just added an excellent article on one of my favourite subjects. Link Building 101 is yet another good explanation of why you should build links to your website, and although regular readers will have tired of hearing about this, I'm going to keep banging on about it forever. One of the best bits is "So what makes a good link?" …the answer being, of course, one from a page or site which is relevant to the search term you're trying to rank for.