Which way do you like to carry your bags? I'm not too familiar with the ITB flap, but I know that the Celine is mainly a hand carry bag. Also, it can get a little heavy. I wanted one and tried one on, but I didn't like the weight and the fact that you didn't have the option to just sling it over your shoulders when you wanted too.
I would go with the ITB in black or marine patent - even it is not real leather this bag looks very elegant, fits a ton, is light weight and is in the lower price range of the Chanel bags! I like the proportions as well.
I'd say go for the business flap!!! i love how the top half has the smaller quilting and the bottom half has the larger quilting and they manage to fit in perfectly!!! if it is seasonal like what somebody said up top go for it as the celine luggage i think is somewhat permanent... also the business flap is slightly thinner, which means it would be less cumbersome than the celine travel