I also struggle with the same decision as you, but on a new ML500. I live in Dubai and White is really popular and Palladium is rare on the roads here, but when I see Palladium, I stare and go wow!
Palladium is my favorite, now and my dealer was really so happy of this choice, it sells like hot cakes here.
Here are few reasons why I like Palladium: because it is a masculine and yet elegant color, goes well with AMG rims or any other metallic rims... and it has an edge over the iridium.
In comparison to white, especially calcite, its kinda lacks luster, in my mind. For sure, it does not show dirt, but when its dusty, it looks like its been sanded down. There is Diamond white, and very nice, but forget matching the paint when you have a chip or dent... If you like extreme contrast, go for white, but I find white with silver rim, kinda off... but with black rims, its nice.
I also have the panoramic roof and I can see how the black against the grey and I want to put some black rims, it will look really hot, and I can imagine this combo out at night, cannot go wrong with Palladium.