It turns out Rick is right.
The size of the home water heater (e.g., 40 gallons, 50 gallons, etc.) is nearly meaningless, as is the warranty period.
The only way the tank size plays any role in the selection process for purely physical reasons. Why? Because both the EF and the FHR already take into account the size of the holding tank so there is no need to even bother to look at tank size (other than for purely physical reasons).
Likewise, the warranty is always less than the average lifetime of a home water heater, which, at 13 years, is vastly greater than the 1-year labor warrantees all the heaters I looked at (from Sears, Lowes, and Home Depot) provided. (Note: The 12yr/9yr/6yr/etc. warranty figures often quoted by Sears/Lowes/HomeDepot are for PARTS! Not labor).
Thanks everyone for enlightening me ... If I didn't know better, I'd buy by the size of the tank and the warranty but now I know they are meaningless figures. The manufacturer WANTS you to look there but in reality, the truthy lies in the FHV, EF, and cost/therm.
I didn't realize you guys knew so much about home water heaters ... but I'm glad you do. In only two days, I was able to take my knowledge level, with your help, from absolutely nothing to being able make basic lifetime cost comparisons given any two home heaters.
Thanks!
Donna