Joyent would probably claim that kvm+zfs would be best. But if you don't have kernel support for jails, then no, using jails isn't better. It's not an option. Oracle would probably claim solaris zones are better (and arguably, they'd be right).
Jails are (as far as I can tell) great -- but not so great that freebsd didn't include a new hvm assisted hypervisor in freebsd 10 (BSD Hypervisor (bhyve)).
