my 2 cents : yes FreeBSD is great, and yes use it. In the end, the SmartOS/Illumos and the FreeBSD communities are quite close.
About Jails : it is made for security from the get go, while Zones were made for segmentation with security too.
The problems of Jails is that there are still a lot of patch lingering around and not being accepted upstream that are needed to bring them up to speed with Zones, especially concerning networking and ressource usage.
Now, i use a freeBSD for my server right now. I would use SmartOS if i had to handle a dozen hardware machine or need to build an infrastructure on top of it.
If you have a handful of hardware servers and not a lot of different loads/jobs to run on to it, use a FreeBSD. If you want a DC/OS or a container scheduler on top of it, use SmartOS.
If you have a strong preference for any of them, go for it.
You can also choose a Linux. Your pick. I am not always a fan, but they have a deep amount of knowledge floating on the web to help. FreeBSD is catching up, mainly due to DO offering them, but SmartOS is still far behind.
It all depends of your engineering needs and constraints.
