Play has a lot more momentum than Lift, examples of this are:
This poll: Top 20 Web Frameworks for the JVM
This report: New app framework popularity report - Rick Astley wouldn't give this up
Mailing list members (~7700 for Play vs ~3600 for Lift) and more than twice its activity on a monthly basis
Forks of the project on GitHub (685 vs 125)
StackOverflow questions (4439 vs 787)
данные на январь 2013