"Which platform should I choose?"
I see this question a lot. It pops up on Twitter about once a day. All three choices have come a long way, even in the past year. Here are my own admittedly biased opinions:
WordPress, the software you download:
You can take Wordpress farther and do more with it than any other choice. It is far more customizable than either of the other two alternatives. There are so many themes and so many plugins available that you can do almost anything with it. If you need to customize it's templates, they are much more straightforward than Typepad's (you cannot customize Wordpress.com's templates).
CONS: Wordpress wants to be installed in a Unix/Linux environment. You can install it on a windows server but the effort is almost not worth it. Even then, in my experience - unless you are a geek - it is unlikely that the installation will go smoothly. I've done it a lot and know where the potholes are. Also, even if you have a Linux server, if it does not already have PHP and MySQL installed then I think there is just way too much to get installed and working. You need to establish your own mechanism and schedule for backups. If for some reason you want multiple blogs you will have to instal multiple copies of the software.
You also need to consider that Wordpress software is frequently upgraded to address security issues and you'll need to be upgrading your wordpress installation from time to time (I've written more on this here.)
Wordpress.com:
I used to strongly recommend against using Wordpress.com. I think that when it's had another year to mature it may be the platform of choice. It is very inexpensive (in most cases free) and since it is based upon the same Wordpress software as you would download (with some changes), it is pretty easy to use. It just works, no worries about trying to figure out what's wrong when it's down, no worries about backups. No software to install.
CONS: The number of themes is growing but still limited. Finding a theme that has (a) a Nav Bar, (b) a color scheme close to what you want, and (c) a customizable banner may be impossible if you want to give your blog a family resemblance with your existing website or collateral. If you wanted to modify the colors (modify the CSS) or map it to your own domain name then they will charge you. WordPress.com does not allow you to install third-party plug-ins, reducing your expansion abilities considerably. Technical Support is almost non-existent. Many of the coolest tools (like Quantcast.com, Feedburner, formspring, AddThis, ShareThis, etc) won't work with Wordpress.com because Wordpress.com prohibits you from embedding snippets of javascript into your blog.
UPDATE: More here
Typepad:
Very easy to set up even for a non-geek. Though there are no third-party themes, they have hundreds of themes to choose from. You can customize the look of your Typepad blog easily by modifying the CSS. Their menubar/navbar functionality is the most flexible of the bunch, you can even have menubar items that point offsite. Excellent (the best IMHO) integration with the most popular blog-related tools (Feedburner, ShareThis, AddThis, etc) It's a hosted solution so you don't have to worry about downtime, backups, etc. Though they are a bit hidden, widgets are available to do polls, have an Amazon store, paypal shopping cart, etc. No software to install. There is REAL technical support (They even hang out on twitter - @sixapart ). You have more control over the choice of font and font sizes within the body of your posts.
CONS: Typepad's collection of widgets is not as extensive as the plugins available for Wordpress. If you want to customize the appearance of your blog (modify the CSS) you have to be at the PRO level which is $14.95 per month. If you want to host other applications (your own online store, for example), you'll need to put that stuff on your own non-typepad site and link to it.) If you need to do really heavy customization then Typepad's underlying template code is harder to understand.
Summary:
So you can see there is no clear-cut choice. I always spend some time with my prospective client, getting a feel for what they want to do now and in the future, and then based upon that I'll pick the one that I feel is best for them. Most of the time that ends up being Typepad.
I almost never choose Wordpress.com. Most beginners do not yet understand the value of feedburner, ShareThis, etc and are seduced by the low price (usually free).
On the other hand, some things just cannot be done on Typepad. Take a look at the slideshow in the right sidebar of this site:
http://www.CreativeTherapyArizona.com
There is no way I could have done that with Typepad. What pushes me over the edge toward TypePad for most clients however is the version-upgrade issue. On Wordpress that is a task that is beyond the capabilities of most non-geek business owners. On Typepad it is a non-issue. I've written more on this topic here.
