I have the Clemence wallet and Vernis business card holder. I would have to say the Vernis is my favorite because it's so small and fits in all of my bags while holding a lot of items. I adore both of them though.
I love my 6 key holder, my zippy multicartes, and my rosalie coin purse. Can't narrow it down to just one! They are all very functional - the key holder for obvious reasons, the multicartes for loyalty/points cards and the rosalie coin purse for coins and I also store my gift cards in there.
My best SLG would be my Cles since use it everyday and it acts as a small wallet on the go for when I want to run quick errands without a purse. I could have enough to decorate a Christmas tree and I'd still have room for one more.