It depends for me. If you're playing a game mode like SnD where it's mostly 1v1 encounters, then use hardened. If you're playing game modes with large groups of enemies, use SoH. For me, the main deciding factor between perks is their main function, and the pro parts are just added bonuses.
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I enjoy Sleight of Hand Pro because I like having the advantage of being able to reload quicker on the guy I'm having a close quarter combat with, but Duel Mag also gives this advantage. But hardened makes the bullets more powerful ie. Being able to penetrate better. Thus making them stronger.
So if playing Hardcore I would use Sleight of Hand, and core Hardened. Both equal in my opinion and I use both.