Opinion for "3 on 6" dental implants vs "All on 4"?

Generally speaking, All on Four will save money and likely more predictable. 3 on 6 is nothing new, it is simply 3 separate bridges, but it requires ideal bone and loses out on what is called "cross arch stabilization". This cross arch stabilization found in the typical All on Four restoration means that bite forces on one side are counteracted by the implants on the other side, providing stability. This is why we can load these implants on the day of surgery.

Both are perfectly fine options and neither is better than the other.

The all on 4 treatment will replace the teeth and gums, if what will be replaced is only the tooth portion then separate bridges can be done.

The answer to your questions depends on many factors. An important consideration between these two options is your own facial structure and what would work for you cosmetically. The "All on 4" option will replace teeth and gums (like a denture), while the dental supported bridges will replace the teeth only. 
There are also pros and cons to getting more or less implants. Sometimes with more implants, you may require extra procedures like bone grafting depending on your own anatomy. The pros of having more implants is more stability and protection for you long term. 
Another factor that is key to the success of your implants is cleansability and the maintenance of your implants. Ask the specialists about the maintenance program they recommend after you get the implants and see what works best for you.