How Many Foundations Does One Person Need?

I guess this all goes back to the "buying makeup for purpose or necessity" post.  I've realized that there are a lot of great beauty products out there.  I don't know if it's possible to say "This is my all time favorite [insert product here]". As an avid beauty blogger and makeup enthusiast, I try new products all the time.  But it's hard for me to say "Ladies, this is the foundation you need.  It's perfect. It does everything." I'll use a product consecutively for a week, then "stumble" upon on of my old favorites, then throw it back into the equation.

It's especially hard when it comes to foundations. To date, I have 6 foundations in constant rotation.

1. Make Up For Ever HD Foundation ($40)

2. Make Up For Ever Mat Velvet Foundation ($42)

3. Make Up For Ever Face and Body Foundation ($38)

4. Bobbi Brown Moisturizing Cream Foundation ($42)

5. MAC Studio Stick Foundation (discontinued)

6. Black Opal True Color Stick Foundation ($10)

Question of the Day: How many foundations do you own and what determines which one you'll use for the day?