for me it's how a word sounds first and foremost, and then how and where it's used. this is where written works diverge from spoken language to an extent due to emotion, inflection etc., but whatever.
ate vs devoured
walk vs lope
red vs crimson
reach vs grasp
Some words are stronger, some more sibilant, some both. Some words are blunt but strong, others blunt and meek. And words can compliment each other, something that becomes more important in poetry than prose: Eater of planets vs. Devourer of worlds. Reaching for wealth vs. grasping at riches. thick forest vs verdant jungle.