I like the Kong Genius my secret santa gave Lucy last year
It's kind of tricky to fill, but it actually takes her a couple minutes to empty it (when all the ball/cubes/etc took around 20 seconds, no joke). You can add extra pieces to it to make it more challenging.
The twist-n-treat is fairly successful here too. I bought the smallest size and screw it down all the way, so that it packs the kibble in and makes it trickier to get out. It only holds 1/2 cup of kibble though (which is fine, that's her whole breakfast)
The balls were annoying, because they'd always end up under the sofa, and she figured out that if she dumps it down the stairs all the kibbles fall out...