Best off set cam sizes for Yosemite?

I am thinking of getting some offset cams for climbing pin scars in Yosemite like Serenity Crack and others. If I were to buy only three, what are the best sizes to get?

Finger size and up. Green/Yellow, Yellow/Clear, Yellow/Red, and Red/Clear are the free climbing pieces I use the most. Now, on Serenity on the most pin scarred pitch you don't get much of anything for about 20 ft off the deck, regardless. But I find the yellow/clear, or a regular yellow alien to be the ticket for the crux 3rd pitch.

the Blue/Green Alien is a DAMN handy piece, IMO.