Buying a water heater is like buying a car - if it was made on Monday it was not as good as if it was made on Tuesday, which was better than Wed, but not as good as Thus, and forget about made on Friday...Meaning: pure luck.
The first water heater I bought was a Reliance for $89 from Builder's Emporium. It lasted longer than today's water heaters going for $500. More expensive doesn't mean better. Today I buy them from the plumbing supply warehouse, they usually sell dented WHs for a little less, I guess they can't find a better forklift driver, who won't dent them, so they discount them.
Since water heaters don't last forever, go for the one on sale. Your chances getting a lemon are the same.