Personally I prefer the New Lock pochette because of the style itself, the New Lock bags are slouchy leather bags which gain its shape over time whereas the Miss Dior is a more structured bag. The pochette also has the chain which can be worn cross body, looped over the flap to be used as a double chain shoulder bag or the chain is detachable so you can use it as a clutch.
The New Lock pochette comes in lambskin or patent leather in various colours for £760, but the only exotic skin on the Dior website at the moment is the Bois de Rose python for £1300.
The Miss Dior bag is at a higher price range than the New Lock, comparable prices to the Lady Dior so I imagine prices will also be higher than the New Lock pochette prices. However, the materials and exotic skins offered on the Miss Dior clutches are fabulous, with beaded velvet, ostrich and crocodile skin to name a few in addition to lambskin
In the end it comes down to your own personal preference, the New Lock pochette is smaller, cute and can be used night or day while the Miss Dior is a more elegant medium sized clutch, but I would advise going to your nearest boutique and asking to see both designs and range of materials available and decide from there