The thing is cards are everyday items, thus not suspicious, as opposed to odd boxes, huge rings, etc... This makes good tricks much more organic, impactful and magical. But that is theory.
Picture the stereotypical magician....
Awkward guy, 3 piece suit, top hat, playing cards fanned in a hand, cane in the other.
The thing you do not want to be.
So when a magician gets out a deck of cards he is directly associated with that, this is why I like non-card openers. But after the contact is established, use everyday items such as playing cards (regular ones, not the super fancy ones, they are suspicious). Give the audience the opportunity to handle the cards to remove all suspicion (that means no heavily gimmicked deck). Be as impromptu as you possibly can.
The only moment I like opening with cards is when they are a tool, not the main focus of the trick, such as an invisible deck (find a good excuse to ditch it as quick as you can).