Undoubtedly the best dual SIM phone in 2016 is the One Plus 3. 99% of previous dual SIM phones were quite limited in their function.
When shopping for a dual SIM phone, you would look for a phone that is capable of using data on 3G/LTE and simultaneously use 3G or LTE on the other SIM in the phone. This hasn’t been the case in majority of the phones that have been around. You were limited to 2G (GSM) on one SIM while using 3G/LTE on the other SIM.
The OnePlus 3 has made some break thru allowing you to use 3G/LTE data, SMS or voice on one SIM, and simultaneously use voice/SMS on 3G on the other SIM.
With the impending shut down of the 2G networks in Canada and the United States, dual SIM phones were essentially going to be single SIM phones practically speaking as the 2G/GSM SIM would be rendered useless.