I am using mozilla with google toolbar and my PR says 2..but when I use an online checker, I got 0. Which one is reliable?
If you're using tabs, sometimes the toolbar will detect the wrong PR of the tabs. I would switch back and forth between the tabs to see if PR changes. Say you visit a PR4 page, then a second page with PR0. Sometimes the second page will display PR4 when in reality its PR0 and PR4 was the last page's PR. It's best to trust a PR website, especially one that lists the datacenters that it accesses.
Who distribute Page rank? Answer = Google, so G tool bar is most efficient tool. But if you find some doubt when data centers are down than you can go for other tool to check your website PR.
I still have PR 2 on toolbar... I don't have tabs..just one page firefox.. url is http://www.myseoblog.net
Any online tool is pretty unreliable at the moment, go with toolbar, or better yet just wait a few days and everything will settle in.