From my own experience:
BLI: Very smooth, very quiet, decent pulling power (unless you add the optional tires), great quality. May require adjustment out of the box, though.
Bowser: Smooth, not quiet but not loud, mega pulling, and good quality. Difficulty to assemble varies.
Spectrum: Very smooth and quiet, decent power, good quality. Some QC issues, but Bachmann has a good warranty.
Genesis: I only have the old Mikado. It’s quiet, good quality, and the smoothest runner I’ve got. Not a good puller though, and many have gear problems (NWSL has replacements). I think newer Genesis is more BLI level.
Mantua: Some are smooth, some are just OK, and they’re quiet, strong pullers. Quality is good, but not as good as Bowser.
Rivarossi: Old ones are smooth runners (after tuning), but not always quiet, and they’re light weight. Newer ones are excellent runners with better traction and quality, but except for the Allegheny and Heisler, electrical pickup isn’t great.
IHC: Smooth and very quiet, moderate pulling, and good quality. Some of the best budget steam around.
Roundhouse: Smooth and strong, but most aren’t exactly quiet. Easy to build (minus the Shay), and decent quality.
Bachmann Plus/Standard: Hit and miss. Some are very smooth, quiet runners with decent traction and a step above IHC in quality and detail, but others have issues with QC and reliability.
Standard Life-Like (like the $20 range stuff): I’m more forgiving than most, but these are bad. LL’s only good steam is the Heritage stuff (which I don’t have, so I can’t tell you about it).