Hi! It seems we like the same bags, as I follow the same threads, GST, Coco Handle, and now Medallion.
As with my other Chanels, once I like a style, I tend to buy multiples. I have four Medallions. The Medallion was my very first Chanel bag, the black with gold medallion. I then purchased three more. I love the Medallion, but I no longer use any of my Medallions mainly because the jumbo-size logo does not speak to me anymore.
Logos are in now, so the price of Medallions has increased. Plus, Bella Hadid was spotted last year with one, so I would think she influenced the recent price increase in Medallions. Prior though, when big logos were out, you could get Medallions for less than $1K. There is a separate thread on "is the Medallion dated" if you wish to investigate more.
Long term, of the three bags you asked about GST, CCH, and Medallion, I would say the Medallion will be the worst investment (I am only aware of these three bags you asked about as I follow those threads, you may have asked about other bags).
As others have said, I buy bags because I love them, not for investment value. I think for a Medallion, you really need to love that bag and that jumbo size logo. If you do, go for it. It's a great style and holds a ton of stuff. I still love this style, but as of now, I can't get past the big logo. Many people love it as big logos are trending for now. I may use one of my Medallions tomorrow and see how I feel.
By the way, the big thing to watch out for when buying a Medallion bag is the handle flop problem. Bags made in France seem to have the handle flop while most bags made in Italy do not, but some do. So in the photos, if the seller has the handles crossed over each other, the seller is hiding the fact the handles flop and hoping a new buyer will not know this is an issue. Just check/ask as those bags should be priced cheaper. Floppy handles may not bother you, but a Medallion's handles should stand tall.
Like this... see how the seller crossed the handles over each other? It's because the handles flop.
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Good luck!