This may a foolish question and I apologize for this in advance.

I have been trying to work out the translation for the summons on the shrine page and I am still rather confused as to what the difference is between Premium and Pick-up summons. Aside from giving different spotlight units, is there any noticeable difference between the two in any way? Strength, Rainbow crystal worth, level, anything?

And following the question above, is there any preference between the two or which one should go for?