I'd go Whitworth myself, but you'd hardly be alone - some batteries considered going from iron rifles to brass smoothbores a happy upgrade.Yeah the Napoleon was a good allrounder and I'm not surprised the Arty men loved them easy to use not many problems unlike the Parrott's and the they had better defensive capability's unlike the Parrott's if I was in the Arty in those times id pick a napoleon crew.
Nosworthy notes that the peculiarities of gun carriage design in the Americas resulted in a situation where rifles were put on top of the carriages of smoothbore pieces of similar bore, which produced a much greater recoil as the projectile for a rifle was about three times as heavy as the projectile of a smoothbore. Thus a 12-pounder rifle would recoil over twenty feet when fired, and the strain this placed on the wheels caused massive damage to them and would result in broken wheels or bent axles much more often than the eminently reliable Napoleons.
It seems that Lee considered the Napoleon smoothbore better in close terrain and for close in defence, and that the rifle was superior only when engaging at long range in open terrain; given the constraints of the weapons on hand he was probably right.
Though the Napoleon smoothbore was actually quite a new weapon (a smoothbore able to handle ball, shell, canister and grapeshot), and had only been invented in France in 1853 and adopted in America at all in 1857. It perhaps represents the final development of the battlefield smoothbore, not an obsolete weapon but one which could compete more than equally in most roles with the new rifles.