ToME: the Tales of Maj'Eyal

Which chant is better from Sun Paladin escorts, the Chant of Fortitude or the Chant of Fortress?

It's character dependent, but Fortitude probably wins out on average unless you know your character is doing the vast majority of its combat at "3 or more spaces away" range.

Fortress is nice for the hardiness. Hardiness is generally harder to get elsewhere than more hp but again depends on the character.