Treats are kind of a trial and error thing. Zoë's snubbed TONS of treats, of course you can't return an open bag.
Her favorite right now is Wellness's Pure Rewards, Venison Jerky flavor. It's the most expensive treat in the store but she loves it!
This may be TMI but here's a bit of a warning using Cheerios, Zoë gets seriously clogged up if she gets more than a few a day.
In fact when she gets diarrhea I give her a few to help her get back to normal. I knew they were good to use and was shocked when she got seriously constipated! Haven't heard of any other dog having that reaction but it certainly can't hurt for others to keep that in mind.