I love Flake White No.1 by Old Holland; lead and zinc.

Old Holland's Flake White No.1 is a lead base paint; Cremnitz, Lead White mixed with Zinc White. Flake White No.1 is a smooth, durable, transparent white which is ideal for mixing color pigments.  Do take cautions when using Flake White because lead is toxic. However, there is little risk when proper precautions are taken. 

Flake White No.1 is similar to Cremnitz Lead White in that it is lead based and fast drying time with a low tinting strength.

Flake White No. 1 differs from Cremnitz Lead White in ways that are advantageous. This is a case where adding Cremnitz Lead White with Zinc White makes the Flake White No.1 greater : 1+1+3.

Cremnitz Lead White, a stiff paint, along with added Zinc White loosens up. .Flake White No. 1 is smooth and malleable whether using brushes or pallet knife.

Cremnitz Lead White's flexibility wins out over the brittleness of  Zinc White. (Zinc White is not recommended to be used on it's own because of it's very brittle surface when dry.) So Flake White No.1 has a flexible and durable surface useful for painting on canvas or panel.

Zinc White's transparency and cool white color wins over the warmer toned white of Cremnitz Lead White. This gives the painter a bright white in the paint box that doesn't overpower. The transparency and bright white of  Flake White No.1 is great for mixing. Flake White  No. 1 brings a brightness and lightness to color mixing.  The cool, dulling effect of Titanium white can be totally avoided by using Flake White No.1.

The disadvantage of Flake White No.1 is that it is expensive. I have never shied away from using expensive, high quality white pigments. White is the most used pigment and a quality white maintains the overall quality of the painting. A high quality white is the support every color pigment needs in mixing. Flake White is my go-to white