Mana regen is no good for Trynd, Katarina, nor Mundo, but otherwise:
Blue: Cooldown or AP (AP helps every hero at least a little, but cooldowns are more universal).
Yellow: Health regen or +Health are the most universal. Dodge is good too but ideally not used by ranged heroes much.
Red: Armor pen is the most useful for those that want it, but critical chance or even crit damage applies to all heroes. Red is the hardest and maybe the first color to diversify in. You really want magic penetration for casters but something else for physical.
Quints: +Health, straight up, is the simplest and useful for everyone, especially early in the game. Movement speed or +XP work for everyone as well.