If you Choose a Fat Tire: 20" Fat Tire vs 26" Fat Tire

A 20" fat tire ebike will usually have more toque, which lets you ride steeper hills. 

A 26" fat tire will be easier to pedal if you do not use as much motor power. 

If you intend on using more motor power than your own pedalling power, you are likely to get better performance and more battery range from a 20" fat tire 

On the other hand, if you intend on using more of your own pedalling power than motor power, you are likely to get better performance and more battery range from a 20" fat tire