If it was my decision, I'd go with 50-gas. If you haven't had experience to compare recovery-rates, I think you may be surprised with gas compared to electric.

Of course check your local rates, but I will be interested to learn if, having the option for water-heat, you choose electric over gas.

I don't see your wife filling any tubs with 40 gallons of 130F water. If she does, you need bigger heaters than you've written about. : )

For new construction, I'd add in a smaller gas tankless for the master area fed by the 50 gal you have. You'd never run out of hot water for that tub if you needed to fill it, and you don't activate the tankless until the tank is virtually depleted, so no energy wasted.

look into the new "Condensing" Gas Water heaters.
They have efficiencies well into the 90% range and claim they put out as much water as a conventional 75 Gallon water heater. AO Smith is probably the best known one , but more new ones are coming.
I heard they qualify for different Govt + Gas Co incentives/rebates.

We will need a new water heater soon, to replace an old conventional 50 gallon gas water heater that uses a pilot.

Since our gas bill is usually less than $13 in the summer, and I'm 68 years old, I will probably buy another conventional gas water heater--we don't use that much hot water and the price of the condensings are around $500 more ($1600) v/s probably around $1000 for a good quality conventional one.

Were I younger and used more hot water or had a higher gas bill, I would certainly go with the Condensing one, and it's still not "Written in stone", that I won't!

HTH's

Gary