I've liked Propel ever since I started working with it in the middle of last year; I personally find it easier and more fun to use than Doctrine or other ORMs available today. I was excited to see recently that Propel's development team had released Propel 1.5 as a beta, with a launch of the new features to come soon.
He points out two of the newer features that he particularly likes - collections and on-demand hydration and model queries. The first lets you hydrate the results fetched as you need them instead of all at once and the second does away with some of the issues that came up with making Criteria objects. You can find out more about these and other new features on the Propel "What's New" page.