So many whites! These are the whites I use in my work. From left to right: zinc white (the most transparent), zinc-titanium white (semi-transparent, semi-opaque), titanium white (plain ol' opaque white), brilliant yellow extra pale (very warm 'white') and cool white (very blue).
Zinc is great for layering and glazing areas like glass bulbs. I use cool white in almost all my skies. And brilliant yellow extra pale is my favorite for a dollop of highlights. Titanium can be flat in my opinion, so I usually only use this one when mixing and I want the neutral white. And zinc-titanium is that perfect middle place for mixing with a neutral white and still keeping some transparency.
That's a lot of whites. And there's even more out there that I don't have. Always on the search for a new color to add to the pile.