Boy, tough choices since they are both gorgeous bags!!! I have the Chanel GST in black with gold hardware --- TDF! However, since I do not have the Manhattan GM and that is on my "NEED LIST"
, I say Manhattan GM!
BUT: If I had a choice between the two and was going to get just one, I'd get the Chanel GST. As much as I love LV, I think the Chanel GST is more unique. Don't see a lot of people with it, whereas I have seen lots of gals with the Manhattan GM.
Since you are a Chanel gal already, go for Chanel!