Got it. So I have the Performance so it probably make most sense to get the 40amp?
If you need, or want the faster charging speed, yes a performance model 3 can be charged at up to 48amps from a level 2 connector. With that being said, the difference in charge speed is unlikely to make a material difference in your day to day usage of the car.
I am saying this as someone who has a tesla wall connector on a 60amp circuit, that can charge at 48amps, the maximum speed the car can charge at on a L2 charger. I got it because I wanted " the best" when I got the car, and I can tell you that, while I am happy I have the best, fastest charging you can get at home, there has not been 1 single time where having a connector that only did (for example) 32amps vs my 48amp would have impacted me.
TL ; DR .. get the 40amp one because you want the faster speed, but know that for almost all instances it wont matter much in your usage of the vehicle, unless you are running a taxi service or are an uber driver or something.