I use a lot of titanium white paint. Loads of it. I tend to mix a lot of it into mixtures and I also apply pure white highlights.
Most of my paints are Talens Rembrandt which come in convenient 40ml tubes. However I buy my titanium white in big 150ml or even 175ml tubes (I also have zinc white in a regular 40ml tube). Generally the paints that come in these big tubes are lower grade, but I have found the Hönig “professional” range of paints available here in Israel or Pébéo “studio” range to be very good. Basically, depending on which shop I can get to, I buy the best large tube I can get.
I recently bought a tube of Talens Amsterdam titanium white (comes in big tubes and I thought that being from a good company, it would be OK even if they call it a student grade paint). I was rather disappointed. It lived up to everything I have read about lower grade paints. My main problem with it is that it is too transparent. When I mix it into other colors I end up using loads of paint and if I want to add a pure highlight I have to put on several layers just top see the white.
Anyway, now I see why everyone says not to use student grade paints. Yesterday I went out and bought another tube of Hönig white. Use artist grade paints!