what version of 1.8 is best for production multi-tenet now?

We are moving to PBX Manager 6.1.1.11 before venturing to 7
We are coming from 1.6.11.
the ISO comes with 1.8.4.2 and we want to upgrade that to the most stable for production in the multi-tenet .

Any feed back would be great!

thanks again

Keith