Which OS are you planning on running? Or is that another part of the consideration? If you're running Solaris, XFS isn't even an option as far as I know. If you're not running Solaris, how are you planning on using ZFS? Support is limited on other platforms.
If you're talking about a Linux server, I'd stick with Ext3 personally, if only because it receives the most amount of testing. zfs-fuse is still very young. Also, I had troubles with XFS once, when a bug caused diskdata corruption after a kernel update. The advantages of XFS over Ext3 definitely didn't outweigh the costs involved in restoring the machine, which was located in a remote datacenter.