I had these exact 2 bags held for me this past weekend so I could compare and chose one. It was a no brainer for me when I tried them both- Mews 100%! I love the look and feel of it, and the more "matte-like" leather. I really think the sagginess of the Speedy would end up driving me nuts, even if I were to get a shaper. My husband did not like the Speedy at all in comparison to the Mews.
Also, Speedy is one of, if not THE most common LV bag. It seems like everyone has one.
Are you looking at the Speedy in DE? I personally am trying to stay away from vachetta.
I was at my boutique today as someone decided on the Mews. It's a beautiful purse! The only caution I might raise is the strap width: it looked like it was the same as my Siena MM, which I sometimes feel is just slightly too narrow. But I love my Siena and truly, the Mews is a gorgeous choice.