This will be "old hat" to most here but I am still feeling my way.
I recently acquired two reefers in CN colours. One from Atlas O. The other from Lionel.
To my surprise, the Lionel car actually has better detailing than the Atlas O Master car.
Specifics:
1/ The roof hatches have realistic rounded corners on the Lionel, AND locking notation. The Atlas hatches are featureless square slabs .
2/ Roof walkway are see through grill-like on the Lionel and simulated wood strips on the Atlas. That may be a prototype issue rather than lack of detail. Same with the brakeman's stand. See-through grill on the Lionel. Etched grid iron on the Atlas.
3/ The grab bars seem better on the Atlas although the Lionel car does have separately applied grab irons all around as evidenced by the paper slid behind them in the image.
4/ Lionel trucks are actually sprung. Atlas springs are cosmetic only.
5/ Reefer doors open on the Lionel. Not so on the Atlas.
Of course, putting Kadees on the Atlas will be far easier than on the Lionel car but I will have to examine future purchases carefully and not be quick to assume Atlas O Masters are inherently "superior" to Lionel cars.
Er . . . does this make me a "rivet counter?"