eBike watts give you speed.
No, not the way I use an eBike... Throttle first.
350W is OK for anyone that wants to mostly pedal and have a little assistance.
Plenty for mid-drive motors that have high torque. These are hill climbing electric mountain bikes or cargo hauling eBikes.
750W is my preference when riding throttle first.
Plus it's the maximum motor wattage allowed for class 1, 2 and 3 eBikes.
Remember, if an electric bike is rated as class 1, 2 or 3, then it's more likely your state laws will allow you to ride the bike anywhere a normal bike can go.
Anything over 750 watts could be treated like a moped or motorcycle, requiring licenses, registration and/or insurance to ride on the street.
Now we have the real question.
And once again, it depends on how you are using the bike...
You'll find the lighter eBikes have 500W motors or less.
And the eBikes with 750W are used with heavier or faster eBikes.
Lets look at the best wattage for each style of electric bike riding.