I have never used Clarizen, but we did a full evaluation of them vs Workfront and chose Workfront. My results summary is included below:
"Clarizen did provide several strong features (e.g. project status report template, add-ons from the apps Marketplace, vacation time approvals reflected automatically in user calendar once approved), but overall it came down to personal preference for our managers' and teams' use for request and project management as well as timesheet entry within a clean, uncluttered UI." ~ which Workfront provided. We also noted a huge disadvantage of managing user licenses for what Workfront calls "collaborators". Workfront allowed us to easily add as many collaborators as we wanted as part of their licensing package, so we could focus on the main users (our team of ~ 30). Clarizen would have meant I, as a sysadmin, would be managing paid licenses for over 200+ who may not use it daily and a user group who could be active/deactivated quite frequently. Hope that helps Tracy Fox Project Manager / Workfront SysAdmin Sykes Assistance Services Corporation