If the gate has two options, should you buy both of them or is it more worth it to just buy the highest tier?
Hi, buying all will help you as more number of stands means more incoming aircrafts. Stands are one time investment n usually give more than 20x profits.
That’s your personal choice.
I normally purchase the highest one for larger aircraft.
But if you purchase both there are more flexibility.
Dont buy all of them at once… do it gradually after you know what you need.
You will quickly learn that some of multi class stands was actually waste of money 
It depends what the stand will accommodate for me. If it is a contact stand that is s/m I will only buy the m and send all s to remote, if there is l/x it’s worth buying both because especially at IAD, there is only so many X pax arrivals.
And, buy them all will make your game crash servals times
If you are playing on calculator from 90s that may be true.
Im playing on iphone 7Plus
Personal opinion, if it’s only s/m, get both, is it is all sizes (s/m/l/x) only get L/X, and then the one type stands are obvious, also if you don’t want small planes to be dumb at gates, only make remote stands S capable