While I've never used Movable Type, I feel confident recommending WordPress hands-down. It works great, is amazingly flexible, and has a marvelous community. Themes, extensions, tutorials, and more all make WordPress one of the best platforms to work with.<p>Plus, if you've gotten used to the variety of post types in Tumblr, there are quite a few good Tumblr-style microblog themes for WordPress from Woothemes and others. They might ease the transition and keep your blog working more like you're used to. You might even be able to tweak a WordPress microblog theme to look like your existing Tumblr theme...<p>Finally, with the changes going on at Six Apart right now, it's hard to say what the future will hold for Movable Type. Could get better, could get worse, but right now it's in limbo of sorts. WordPress.org (and Automattic) are doing great, and I can't imagine that changing anytime soon.