For a whole house application gas water heaters are the least expensive compared to tankless electric water heaters. For electric tankless water heaters probably you would need to run another electrical service for an electric on which most take 180 amps of service.

240 208 VOLT ELECTRIC TANKLESS HOT WATER HEATER NEW US $259.95

ADK-12 - American Heat Electric 12KW Tankless Water Heater US $208.50

ADK-9 - American Heat Electric 9KW Tankless Water Heater US $208.50

Ecosmart ECO 27 kW at 240 Volt Electric Tankless Hot Water Heater US $544.50

RA18 POU seisco electric tankless hot water heater RA-18 On Demand Electronic US $300.00

Seisco RA-28 Electric Tankless Water Heater US $764.10

Seisco RA-32 Electric Tankless Water Heater US $787.50

Seisco RA-18 Electric Tankless Water Heater US $697.50

Seisco RA-14 Electric Tankless Water Heater US $539.10

Electric Tankless Hot Water Heater - Instant On Demand - 7 GPM Whole House 27kW US $544.50

Eemax Tankless Electric Water Heater Commercial House EX320T2T US $499.00

New Seisco Electric Tankless Hot Water Heater RA 28 model US $819.00

Electric Tankless Instant On-demand Hot Water Heater 18 US $449.00

Electric Tankless Instant On-demand Hot Water Heater 27 US $549.00

Electric Tankless Instant On-demand Hot Water Heater 24 US $539.00

Electric Tankless Hot Water Heater - Whole House - EcoSmart 27 - BRAND NEW! US $499.99

SANTON 9 KW Electric Tankless Hot Water Heater US $202.00

AQUAH 18 KW ELECTRIC TANKLESS WATER HEATER US $324.95

18 KW Electric tankless hot water heater US $333.99

ELECTRIC tankless water heater US $425.00

Ecosmart ECO 27 27 KW at 240-Volt Electric Tankless Water Heater Patented S US $449.99

GE Hybrid heatpump GeoSpring water heater electric GEH50DNSRSA beats tankless US $1,499.95

Rheem RTE-13 Electric Tankless Water Heater - 4 GPM US $299.00

Bosch RP27PT Electric Tankless Water Heater US $500.00

Stiebel Eltron Tempra 20 Plus Electric Tankless Whole House Water Heater, 240 V US $539.95

Bosch RP27PT Powerstream Pro Electric Tankless Water Heater 26.85 KW 240 V US $675.00

Ecosmart ECO 18 kW at 240 Volt Electric Tankless Hot Water Heater US $434.50

Ecosmart ECO 11 kW at 240 Volt Electric Tankless Hot Water Heater US $269.50

Tankless Electric Water Heater 8kW - Ecosmart ECO8 US $269.50

Titan TANKLESS Water HEATERS Electric N120 BRAND NEW US $205.00

Seisco RA-28 Electric Tankless Water Heater 28 kw US $880.00

Seisco RA-22 Electric Tankless Water Heater 22kw US $870.00

Seisco RA-18 Electric Tankless Water Heater 18kw US $870.00

Titan TANKLESS Water HEATER Electric N160 NEW US $315.00

Seisco RA-32 Electric Tankless Water Heater 32kw US $890.00

Bosch Powerstar Electric Tankless Water Heater US $229.26

USA ELECTRIC TANKLESS WATER HEATER 15 KW US $325.00

BOSCH POWERSTAR AE115 AE 115 ELECTRIC TANKLESS WATER HEATER *NEW* US $399.00

Rheem 5 GPM Electric Tankless Water Heater RTE 27 US $816.52

3 GPM ELECTRIC WHOLE HOUSE TANKLESS HOT WATER HEATER US $429.99

1

However, there are people who are quite comfortable with electric water heaters. Then you must be looking at a good brand , and you need to get the biggest one that you can afford. 24kw or bigger.
Overall both work great. They do operate just a little different than a conventional tank system, but you will get the hang of how they work.

The point against tankless electric water heaters is that you would have to retrofit a lot of electrical work compared to the gas, which require some electrical work. It is pointed out that on new houses in Texas, they cost about $2,000 installed (unit itself is about $1,200). However, the more units that you install the lower the price per unit should be.

Another point in favor of tankless electric water heaters is that they are very safe compared to gas tankless water heaters. They are easy to install and work well. You can fill your tub all the way and never worry about hot water running out. You can have 10 guests over and not worry about the hot water running out! They simply provide endless hot water so you can shower all day if you want and they never run out. So when rating electric versus gas tankless waters, you will find both useful for their individual merits.