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ASTM light-fastness ratings are a useful indicator whether a given pigment fades as it decays, so that's a good starting point. Light-fastness is not the only consideration, however. Pigment load, i.e., the amount of actual pure pigment in a given paint, proportional to the volume of inert extenders (clays, waxes, stearates, etc.) and the nature of the binding vehicle ultimately determine perfomance over the long-haul.
This isn't to say that "good paint" should have none of those additives; some pigments cannot be made into paint without them.
Having tested to my own satisfaction the common vehicle oils, (and a few uncommon ones!) I found (surprise, surprise!) that high quality linseed oil produces the toughest, most elastic clear and durable film. Walnut oil is an acceptable runner-up. Safflower oil is for all practical purposes not a drying oil at all (i.e. one which forms an irreversible polymer through oxidation) and requires the addition of siccatives to perform adequately as paint. The film it produces is weak and granular. Poppyseed oil is not much better as a film, and reverts to a "goo" in ambient heat (87F+) . Consequently, I look for paints mulled in linseed oil, and that's getting tougher since major brands like W&N have "converted" to safflower and blended oils.
Gamblin uses linseed, as do Old Holland, Williamsburg, Studio Products, Vasari and Doak to name a few. M.Graham uses walnut oil.
There's nothing wrong with mixed tube pigments (as in the W&N Perm. Crimson Lake - PR-177 & PB-29) so long as you know you're starting with two or three different pigments when you squeeze the tube. As I feel mixing more than three pigments diminishes color clarity and brilliance, I try to avoid it on the palette. (tough to do, though!)
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