Having read them both, I am still partial to The Story of Greece. It is so readable and shares more details than The Story of the Greeks, without being tiresome. The stories are still fairly short and I think they are engaging (keep in mind that I find history fascinating, lol). According to Heritage History, if you were to print out the pages from both on single sheets, The Story of the Greeks is 115 pages and The Story of Greece is 167 (several of those are going to be great illustrations).
My dds MUCH prefered it to the FMoG, but again, I think that was because we started with no idea who was who (or what) so The Story of Greece made what stories we had read tie together much better in a story form.
You know your daughter, so you can try it on her and see. If she didn’t go for the extra details, you really could try On the Shores of the Great Sea and add Stories from Greek History by Ethelwyn Lemon. I haven’t read it yet, but it sounds like it would work. Here is a link (it prints out to 36 pages):
http://www.heritage-history.com/www/heritage-store.php?pid=ebook_lemon_greek_1
My dd was quite sensitive to the whole false god thing too, and felt impatient and sad about those stories. However – she LOVED A Wonder Book by Nathaniel Hawthorne – which is based on the stories of the heroes. But it is plainly told as stories and not so much as a “true story” thing. It really has a different feel than the others that I’ve read so far (I’m reading through the YC and HH collections). She is asking when we will start Tanglewood Tales. These might be more sucessful with older children than 6, though.