from my limited experience:
i have some walters, bachmann, bachmann spectrum, athrean genesis, RTR and older Blue box models. + toy grade tyco F7
if you ask me (i'm not very demanding in this) the level of detail is amazing on even the less detailed walters. i'm completley blown away by detail level of athrean. as for the premium genesis and spectrum i'm simply out of words.but those are obviously more expencive.
as far as i understand atlas is on par with athrean and kato is somewhat higher end.
I have Bach, Kato, Proto 2k, atlas and Athearn and found that Kato, and Proto have the best detail. The great thing about this hobby is that with a little work you can increase the detail on any engine you own. For example, I purchased a second hand loco from the LHS for 20 bucks, after 3 days of detailing, painting, and customizing (not to mention throwing in a DCC card and lights) the engine looks perfect.
I forget which issue it was, but model railroad mag had an article where a gent put on ditch lights on a Soo line engine.
One of my favorites to run is not that high quality or detailed loco. It is a regular series Bachmann 2-6-2 Prairie. It is detailed enough to be interesting as it runs, has decent pulling power for its size, can turn on my 15 degree corners without issue. It is just a solid and quiet runner. And it was on $10 on EBay. I also really like my Tyco Chattanooga. It was made the year I was born. I wish I could find other makers of tender drive locos. Only issue with mine is that the main pinion gear came loose. Will have to fix that when I get time.
You would have better luck with powerering a piece of rolling stock than fixing that grear.That is the weekness to the engine. Plenty on ebay though. I prefer a cast boiler and the old Mantua's fit the bill. They still make them both with plastic or metal boilers. Parts are available. I cleaned up a Pacific once for a friend. Nice engine with worm drive.
Fixing that gear would make intereting reading.
PS I have never seen a red box Rivarossi. What time period is that?
T-Man, I believe that the Rivarossi "Red Boxes" started around 1995 or so. I have a plethora of them. Around 10 or so, maybe more. These engines can pull some mighty long consists. And I place my decoders in the cab where the old style models once had their motors if the fit is too tight in the boiler.