Good question. I have an untested belief that sitewides would be better for building PR, but not by much. This is based on my also untested belief that SE's tend to ignore more than XX links from one site to another. I have some sitewide links pointed to one of my sites, and Yahoo showed many of them for a while, but then started showing fewer and fewer. Google did almost the same thing. I can "Show the omitted results" when I click the link at the end of the search to see all the links, but the fact that Google doesn't include them automatically tells me that Google recognizes that the links are all on the same domain. It'd be easy to ignore all but a few of them and only use a handful when calculating things like PR. One thing I am wary of is that sitewides may get reported as paid links. This could create a few headaches. Obviously with a single page link this is not a problem. But since you know your link is only on one page, you also know you're only getting PR from one page.
From what I understood, sitewides links are for example those showing on blogs sidebars & forums signatures? BtW, what's a "serp placement"?
SERP stands for Search Engine Ranking Position , and it's the position on which your site can be found for a certain Keyword . Example : your SERP is #1 for the kw twaikiti ( that word doesn't exist , i made it out to point an example ) . Having sitewide links , means those links will show up on every of your pages , so when Google comes and indexes them , they will count as backlinks , but take note , they will lose most of their weight because of the fact they are all on the same domain .
Thanks, now that I know what those letters are for it's clear. Yep, something like what I said, links in blogs sidebars show in all the pages of the blog, it's better to have one link in different domains than to have many under one domain.