I have the Sienna (in luggage) and I adore it. It's a really well-made bag- the leather is excellent and the bag is very sturdy (I can be a bit hard on my bags). I've become quite the Kooba fan as a result.
As for your choices, I'm partial to the Sienna, but I think it depends on what you want to use the bag for.... do you want to be able to carry a lot (the sienna is really roomy)? For colors, I'm partial to the espresso, but the black is lovely too- which do you think you'd get more use out of with your wardrobe?
Also, if you do decide to get the Frankie, it's on sale at active endeavors: http://www.activeendeavors.com/product.asp?catid=3483&pfid=AED09312
HTH- I'm sure you'll love whichever bag you decide to get!
This may be because I live in Los Angeles and see lots of girls with the Siennas, but I'm really partial to the less-exposed Frankie. I also prefer the symmetrical, rectangular shape of the Frankie.
Oh, and I can't believe I dared to look at the Revolve site, because now I want THIS. It's the Kooba Kendall in Berry...$550. *sigh*
i have the sienna and i love the sienna. i think the frankie is too small for my tastes. yes the sienna is knocked off, so is my bulga, but you can EASILY spot the fake ones, it's not like LV where they've gotten soo good with replicating the bags. so i wouldn't be worried about it being knocked off, more about the size that you like. that's just my $.02.
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"i tell you one lesson I learned
If you want to be something in life, You ain't gonna get it unless, You give a little bit of sacrifice, Oohh, sometimes before you smile you got to cry.." -The Roots