We simply don’t have enough data to compare. My hunch is that most politicians achieve less than 20% of the commitments they make during their campaigns, most of which remain forgotten in the depths of Google and recycled newspaper.
That may soon start to change thanks to a new trend in the online transparency community. The first website I’m aware of that set out to track the fulfillment of campaign promises by politicians is Mumbai Votes, which was first created back in 2004. (You can see Namita Singh’s interview with Mumbai Votes founder Vivek Gilani at the Technology for Transparency Network.)
Then in 2009 PolitiFact launched the Obameter, a compilation of President Obama’s 508 campaign promises, categorized by topic and the current level of fulfillment. (So far Obama has kept roughly 34% of his promises, which puts him well ahead of Chile’s Piñera.)