Your question woud be a good one for the Classic Toy Trains Forum, Where mor epeople who know about O scale would be likely to see it.
Lionel, Mikes Train House and K-Line and now Atlas are the "big" companies in O. Most of their products are 3-rail. All Atlas cars and locos are also available in 2-rail
Lionel, Mikes Train House, and K-Line make both "tinplate" and "scale". With MTH and K-Line their labeling distinguishes which are tinplate and which are scale..
The difference between tinplate and scale isn't quality, its size (tinplate is usually smaller) and detail. Tinplate is a toy in the tradition of the pre WW2 trains. The scale is a model.
Atlas is scale.
I have converted some MTH (scale) and K-Line (scale) freight cars to 2-rail. Converting MTH is difficult because of their design. Most K-Line is easier to convert since K-Line makes 2-rail trucks that fit most but not all their 3-rail cars. MTH has offered some of their locomotives in 2-rail.
Another company in O scale is Weaver (scale). They make both 3-rail and 2-rail cars Their cars are nice models but not as heavy and durable as the others. I am not familar with their locos, but hope to have a 2-rail VO 1000 shortly.
There are many fine O layouts tinplate and scale 3 rail The tinplate layouts are usually lots of seperate loop of track with lots of independently running trains in the old toy train tradition. 3-rail scale usually operate like model layouts in other scales.
Lionel has changed hands a number of times. The quality depends on the when it was made. Some owners have gone cheap and others for quality.
MTH and K-Line have overall been good quality so far.
I play with O scale 2-rail. There is allso Proto48 which is O scale 2-rail withe the corract track gauge (4' 8 1/2") Traditional O scale 3-rail and 2-rail is 5' gauge