I have a SteriPen, a Sawyer in-line, and I always carry a few individually wrapped tablets as a back up. The Sawyer (IMO) is by far the best combination of convenience, sustainability, cost effectiveness, and reliablility, and the weight difference is negligable. So what did I take on the JMT last year????
Why? The water is the Sierras is arguably the most refreshing in the world, and the SteriPen is the only one of the options mentioned (other than not treating) that does not affect the taste of the water. It may seem silly to some, but to us it was one of the simple pleasures of the trip. I wouldn't have thought that the Sawyer would affect the taste, but it does. For the local mountains and such, I use the Sawyer.