best fuel system cleaner?
 

Is there one that is head and shoulders above the rest?

Or do they all pretty much do just as good a job as the others?

1 Techron concentrate

2 SeaFoam

Techron, but double the amount.

what are the symptoms to use such product for treatment?
is it the same of fuel injector cleaner?

Techron is a solvent which is designed to clean the fuel system of varnish and fuel deposits, including the stuff that sticks to the back of intake valves. It will not clean up a rusty fuel tank or lines.