Would there be a reason to cast a higher level version of a spell if there is no difference between it and it’s lower level version?
For instance:
Speak With Animals II seems to be the same as Speak With Animals I. There are other examples with other spells, but is there a reason to cast the different versions? Cost seems the same, effect seems the same…
Shield is the best and most common answer to this situation as it only ever adds 5 to AC, but if that 5 AC is the difference between your character going down then it’s worth a 2nd or even 3rd lvl slot for an additional cast.