I don’t have a favorite brand per se. I’ve found that there are certain colors that I like in each brand so I’ve got a mix. In tube paints, I’m heavy on the M Graham side because I do like many of their colors, and since they are a local company in Oregon, their paint is usually $3 or $4 cheaper than the other brands. Unless the brand has something that REALLY makes it stand out, I’m likely to go with M Graham for that reason if no other.
In pan paints, I haven’t tried many of the professional brands – I’ve got the usual suspects in the student line – Cotman, Yarka, even Koi. But I’ve only tried Sennelier and Winsor & Newton in the professional grade so far. Price has kept me from expanding my list, but it will only delay not stop. I will prevail in trying every brand under the sun – even if I have to live to be 1000 years old!