The 1860 Army was Colt's first "holster" pistol (revolver) in .44 caliber. The previous Dragoon series were called "horse pistols" and for good reason - topping 4 pounds, these were better carried on the saddle versus on one's waist. But the 1860 incorporated a lot of interesting new features, included a stepped cylinder, allowing it to be used in a smaller frame (Colt's .36-caliber frame), the creeping loading lever, and better metal.
The 1860 Army was very popular, so Colt decided to incorporate some of these improvements in the next generation of their Navy revolver, the 1861 Navy. Some thought it was unnecessary, since the 1851 Navy in .36 caliber was considered by many to be the best fighting handgun of the time. Many modern day cap and ball enthusiasts consider the 1861 Navy to be the pinnacle of the black powder percussion evolution. I myself prefer the .44 caliber 1860 Army, also because it has a larger grip which better fits my hands.
Here's a view of both, with the Army on top and the Navy on the bottom:
As you can see below, the Army on the right does indeed have a larger grip. Apparently though, the Navy frame better fit the majority of the people at the time, because Colt essentially copied it for their famous Single Action Army, their first purpose-designed and made cartridge revolver.
Here you can see the stepped cylinder versus the straight cylinder. On top is the .44 caliber Army; on the bottom is the .36 caliber Navy.
Another difference between the two models is the grip-frame material. As you can see, the 1860 Army utilized brass for the trigger guard and lower grip frame; the 1861 Navy used blue steel.
And finally, the big difference as seen by a view of the bore. I wouldn't want to be hit by either - but I would want to be hit less by the .44 caliber on the right than the .36 caliber on the left!
Just in case you prefer a more subdued finish than that what seems to me overly bright CCH.