I like the Lake Country 6" backing plate and 6-1/2" pads -- I've got a full assortment, but what you need depends on what your challenges are and can be influenced by what products you're using.
As a minimum, I like a yellow cutting, maybe an orange light cutting, a white polishing pad, maybe a black finessing and a red waxing/final finishing pad.
If you're using a one-step cleaner wax, you can just use a black pad.
Certainly you won't go through every pad each time you wax, but having a choice is nice.
Here's the first set I bought:
http://www.detailersparadise.com/Vie...-1225212614088