I've used the SteriPen for a number of years. While I like it, it does have some drawbacks - first is the battery life, even if you use the Lithium batteries, and second is that you have to hold it for a couple minutes per 2 liters of water. The Sawyer in-line filter is really convenient. I've used both on numerous pack in hunts and long distance backpack trips and like them both.
If you go the Steripen route, bring a Gatorade bottle. The top of the Gatorade bottle holds the steripen perfectly, freeing your hands up to do other chores (make dinner, set up camp, etc.), since it takes two minutes to filter 2 liters of water.
Lastly, I'd recommend carrying a bottle of either iodine tablets or the slower working sodium chloride as a backup. Bring some powdered Gatorade or Nuun tablets to mask their taste.