I use WordPress, after using bMachine previously. I find WordPress to meet most of my needs. However I post alot of code and I have not found a blogging tool that makes it easy to paste without the tool itself messing with the layout (not handling backslashes, getting rid of carriage returns, adding carriage returns, formatting, etc.).
I found a good review of many of the free blogging tools here: http://www.asymptomatic.net/blogbreakdown.htm Check it out for yourself