I bought the Thames GM in Damier after considering the Hampstead and Galliera. I found the Thames to be more subtle than the Galliera (my botique said they could SO the Galliera in Damier which really surprised me) plus the Galliera PM is pretty big. I am EXTREMELY happy with my choice; it's a great bag, roomy without being oversized and very comfy. Also, it is a little different; I am beginning to see so many (real and fake) Gallieras everywhere. The Hampstead is also a great bag, but I found the top to be too open. Good luck with your decision!!
I bought my Tate/Thames GM on it's very first day arriving to the boutique which will be 2 years this October and I still love this bag. I too was considering the Hampstead but the open top just turned me off too much.
This is my work horse bag and I just love it so much and I think it is at a great price point for a roomy zip top shoulder bag and I am surprise that it is still not that popular especially when it is very similar to the Galliera and it seems every single person out there wants the Galliera in damier.