Which one is compatable water heater to Rheemglas fury Model#41V50?

You have 6-year 50 gallon gas water heater:
42V50 would be the newer model number. They make tall and short models.
http://www.rheem.com/product.aspx?id=CC643E03-4C15-4775-B139-E504A95651F7

All brands of water heater are good.
So any 50 gallon gas water heater from local box store or hardware is good product.
Tanks with longer warranty last longer. So 9-year and 12-year water heater will last longer, unless you have very hard water or odor in water and need to change frequently.
I recommend avoiding water heaters with electronic controls since they are not protected from power surge and can cost more to repair.

Additional resources:
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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