I vote Tiffins. I liked the different styles of the individual rooms in Tiffins, which also kept the restaurant a bit more quiet and intimate than the big open room at Jiko. I liked the food equally at both restaurants. We had significantly better service at Tiffins, but honestly, that is so variable at any restaurant I can't rule out Jiko for one bad server (although it was pretty bad - no drink refills, no cleared plates, a huge wait for the check).
Wonder what you wanted the staff to do? Disney World is a family-friendly resort, and they are not going to kick out a family to make the meal more enjoyable for another paying customer. The risk of this is equally likely at Tiffins, BTW--there are tons of kids there; it's just a feature of dining at Disney. I guess the only way to avoid it really is to schedule dinner earlier in the evening, as I imagine the number of fussy kids increases the later at night it
When the kids are roaming around tables disturbing other diners and causing safety issues I expect a Disney to exert itself so that all paying customers can enjoy the meals they are paying for. And frankly I would like parents to show some common sense and courtesy.