I ain't no expert.
But I have several nickel handguns. I even have, had and still have, Uberti nickeled revolvers. The Italian guns are not supposed to be as well done as Colts and Smith and Wessons.
My Ubertis have held up well with Cowboy Action Shooting and being shoved in and out of holsters. No flaking of finish, no wearing through of finish.
I first use a brush to clean off any residue so as to not scratch the finish when I go to wipe/brush off powder stains, etc.
I use Break Free in the bores and chambers and on the outside as it is supposedly not a threat to nickel finishes [watch someone post here..."Yes it is!"]. But I use it sparingly and clean it off quickly.
Supposedly, even if your nickel finish is showing no visible deep scratches, pin holes, or big holes...in other words "pristine", the continued use of Hoppe's #9 [or any other invasive cleaner] will, over time, work its way into unseen crevices and utlimately cause flaking. Whether true or not why take the chance? I do know that Hoppes will eat away nickel to the bare metal if left on long enough.
The face of the cylinder will acquire a lot of black marks from powder gases, lead, and just plain bullet "stuff". Do not try to clean that off harshly. I use the least invasive method first and progress to a certain point. If, after that, the front of the cylinder is still stained, I go no further. What I do is clean with the Break Free and a toothbrush that has its bristles cut short. If that is not enough I might go with a copper brush, maybe, if I want to go that far. The black cylinder face is [to me] preferable to a cylinder face that has the nickel cleaned off by harsh methods.
NEVER use a lead free cloth on the cylinder face. NEVER use a lead free cloth anywhere on a nickled handgun, except in the the bore. The lead free cloths will take off the nickel [supposedly].
After the weapon is clean, if I oil the exterior I use a soft rag soaked in Rig, or a suitable replacement. I CHANGE THAT RAG OFTEN, as in when it even "hints" that it is getting dirty I toss it. There's another thread going on the Forum about silicone cloths. I posted that I don't use them anymore, they pick up grit, but then any oiled rag will.
You will see nickeled handguns that have a lot of minute scratches in their finish, I suspect that is due to using a gritty oil rag/silicone cloth.
If the nickel finish is a bit tarnished [some say even cloudy or frosted] a good metal polish like Mother's Mag or Flitz, USED SPARINGLY, will shine it up. If there are any scratches the polishes will not take them out, unless they are very, very light.
As an aside, I have a nickeled Colt Python that has wear spots on the barrel and the cylinder flutes showing the copper underneath. I used Mother's Mag to polish it overall and it "appeared" to blend the copper and nickel to where it "appears" to look better. Something to remember if you find a worn, nickeled gun you just have to have.
Here's a some pics to wet your appetite. I think that many of the Smith and Wesson revolvers lend themselves well to nickel in appearance. However only a few Colts appear "nice" to me in nickel, mainly Pythons, Diamondback, and of course the SAA.
The last one is a Uberti/Beretta "Laramie", a somewhat copy of the Smith and Wesson New Model Number 3.