cheap hot water tank failure after 3 1/2 years - expected, luck, installation problem, acid water, pressure cycle?
Given that the last two also failed in the ~3 year timespan, I'd say either 


you and the last guy have a strong affinity for bottom-shelf big-box cheapies
there is a quality problem with your water
there is a quality problem with your fuel


Assuming the pinhole developed in a non-combustion area, that would point to the water.  I would have it tested (which water treatment sellers will often do for free). 

I would also have a close look at the anode.  If it is relatively intact, then changing the anode won't help. If it is massively corroded, then you'll need to make "changing the anode" an annual affair!