The Caliber 2385 is based upon a Frederic Piguet 1185, and is a self winding chronograph movement finished by AP. It is commonly used in the Royal Oak Chronograph.
AP's in-house Caliber 3120 was launched over 10 years ago now and is a self winding movement frequently used in the Royal Oak series, also the Offshore Diver (non-chrono version) uses this movement. It features hours, minutes, center seconds, and a date.
Better? Always a tough question. A closer comparison would be the AP Caliber 3126, which is used in chronograph Royal Oak Offshores. It adds a module to the 3120, many likely prefer the integrated chrono caliber 2385 from a design standpoint. Function wise, I have owned all these movements and enjoyed them equally. AP's in-house movements definitely provide a longer power reserve - 60 hours versus 40 hours on the 2385.