I have always used chiffon cakes for wedding cakes but I've been told by some of the biggest names in the baking business that they use butter cakes.

This is what I have learned so far from google

CHIFFON CAKES:
light cake
moist
does not dry out in the fridge so can be used with fillings that need to be chilled
lack of flavor compared to butter cake

BUTTER CAKES:
heavier cake
moist but dries out and loses flavor when refrigerated (not good for fillings that needs to be chilled)
rich in flavor
great for storing at room temperature

I am making a cake this weekend for a wedding/birthday.
One is a 4 tier, vanilla with vanilla cream covered in butter cream
The other is a 2 tier, chocolate with chocolate mouse covered in butter cream
As you see, I have to refrigerate the cakes (and will be doing it overnight) with simple syrup and deliver it in the morning to be iced at the location of the event. There for the cake will be going back in the fridge for another 2 hours until the buttercream sets.
After that, the cake will be displayed in the venue with a/c but probably won't be turned on because the temperature will be in the low 70s that day.

Even though I have found some answers on google, I am curious to see what everyone else prefers.
Thank you.

I think that you should go withe cake that you know best. Two days before an event isn't the time to be changing up what was ordered or what you know what works.

Why are you frosting on site instead of delivering a completed cake? Are you traveling a long distance with the cakes?

Thank you, I think you are right. But I would like to know what other bakers use.

I am delivering the cake. The venue is about an hour away. It's for a family's friend so everyone was really nice about it. I will have the kitchen to myself for about 2 hours before the catering company comes in.