Which is the best bathroom heater for my shower ?

First, no use for a bathroom heater without safty approval.

Second, buy what is the most suitable, not the most expensive.

There are many functions in one bathroom heater. Some additional functions are useless for you. Choose the one suitable for you without unnecessary functions.

Third, observe the style, quality and brand.

The style should match with the color of your bathroom. You can go on a  sample test before purchase to check if it is featured with good heating effect, quick fan speed, and low noise.
At last you are suggested to choose a unit with package, on which company name, address and contact information etc are written .