roughly speaking...
exterior would be more effective due to reflecting sun on the exterior, preventing the window glazing to heat up and radiate heat, downside is harder to install and susceptible to the elements being outside.
both will decrease the amount of light let through (it's tint duh) so if you have newer windows with low-e / low solar heat gain already built in, it's like tint on tint
another option (depending on building orientation) could be adding a slotted awning if relatively easy to your home.
of course the simplest for anything is interior, whether that's solar tint or solar blinds, etc. I basically just put blinds up...
i'm trying to look for a bug screen type of tech where i can see through and it casts shade but can't find where i can buy a roll myself and make my own 'bug screen'