Persuasion is sweet, haggle is useless
And I've always felt the opposite. I guess it comes down to a difference in playing styles.
While I love the game, I can't stand the AI governing followers' actions; therefore I usually play solo. Haggle is extremely useful in Shrouded Hills and the first trip into Tarant, when money is still extremely tight and being able to sell anything to anyone confers a huge early-game advantage.
(It takes expertise in Haggle to do so... which means if you play as a gnome, you'll only need to spend a total of two character points on Haggle, and none on any extra WP!)
I rarely take more than two ranks in Persuasion, and I do so not for the followers but for the extra quests and gameplay options they unlock. (Listening to Lukan completely butcher the English language, for example, remains one of my laugh-out-loud guilty pleasures.)