You may also want to consider your breaker panel and how much capacity you have remaining -- I don't remember the formula for what size breakers are needed for those EVSE capacities (surely others on here do and will chime in), but if you buy a 32A EVSE I think you can use a 40A breaker for that, whereas with a 40A EVSE you'd need a 50A circuit (again I don't remember the exact specs of how much larger the circuit needs to be, surely the licensed/installing electrician would) and that could be a factor for you depending how much "room" you have left on your panel.