Oh. that's a toughy. I love my pochette croissant. Although it's shaped weird at first glance, I like it once I tried it on. It has lots of space to put all your essentials in despite its size.
I'm really fond of the mini pleaty too although I don't own it. I think it looks great in green (goes so well with everything!!).
I think if I have to reallllly choose between the two, I'd go for the croissant b/c you can dress up or down with it.
1. B/c you already have something from the denim line.
2. It's a really unique/young shape that you can't reallly get from other bags.
3. I love the buckle detailing on the strap.
The only thing that might deter you from it is that it looks kind of small, and will probably only allow for the essentials (wallet, keys, cellphone ipod). Let me know what you choose! I've been eyeing the Croissant for awhile too =D