the links section of Google sitemaps is helpful, but not very accurate and takes ages to update, I'd give it about 4/10
depends upon ur level of expertise, if u are a noob, its good as u move on, it starts becoming a little irrelevant than u come place like this and visit it (GWT)once in a month
I don't use Webmaster Central for checking links, I use it to see what keywords bring me traffic and if crawler has some troubles with crawling my site. btw. that link section is good, I can see exactly how much backlinks each page on my site has got- and this is good.
it's just abit useful ,,,, you get some idea .... but it's not too accurate .. i have seen my site ranking #2 for some popular kw but when i click on it .. i'm not even ranked in the first 5 pages ... and more over ... updates is too slow ...