I use the built in Speech Recognition, you do have to make sure your cursor is in the right place but it seems to work fine for me, I copied my speech profile from my windows 7 machine and its all good a little re-training because with the surface i'm using the built in mic and not my wireless headset.
you are using the Pro right?
Pull up the Charms bar (swipe from the right edge of the screen) and tap search. Search for speech under Apps. First time you launch it will walk through the setup & tutorial. Following it will launch the Speech Recognition applications.
The built-in function is all you probably need for the use you are considering but Dragon is also an option. In fact with the Pro there are many options since you can download and install a variety of software dedicated to this purpose.
I'm surprised how non-sucky WSR has become. I'm a big user of Dragon, which is fabulous (and still better) but requires 3G of disk space and takes a couple of minutes to start up. by comparison, WSR loads in a few seconds.
just be sure to do a training session or two, and let it read your files to find new words and learn your writing style. helps a ton.