I use wordpress.com - mostly because I like the ease of use and customizable themes. And they keep adding cool new features all the time.

Used to be on Moveable Type but like many others, I made the move to WordPress. So far so good. Wordpress has a few quirks and minor annoyances, but being completely free helps me overlook the problems.

I'm still on MovableType, but never got around to upgrading to 3.x.

I had a choice to make: WordPress or Movable Type (the platforms offered by my web host). I chose WordPress because it was easier to integrate into my site. Details are here: link
Other posts in my blog deal with getting the WordPress custom permalinks working, in order to improve my search engine rankings.

I'm using WordPress. It's pretty easy to customize, and there are a lot of plugins... so many in fact that it's kind of crazy figuring out which ones are any good...!