Hello Centurion,
I’m going to assume you’re talking HO scale and preface my list by admitting that I run DC.
Atlas-well detailed, smooth quiet runners (I don’t have any sound equipped ones), diesel locos late50’s-modern locos.
Athearn: Genesis- their top of the line diesels (late 50-'s to modern),steam engines sound equipped locos are well detailed, good strong runners the sound system(s) are pretty good (depending on how demanding you are on sound accuracy and quality). Ready to Run is their mid grade line of pre-assembled locos-good strong runners not quite as detailed as the Genesis line but a cut above the Blue Box line-no sound sysrem(s). Blue Box their basic line some minor assembly required (handrails,couplers) good runners can be noisy, wildly varying speeds between the various locomotives, you want sound and DCC it’s either do it yourself or pay for someone else to do the job. Usually good reliable locos.
Kato - some assemby required (handrails, grab irons),smooth quiet runners, well detailed, no sound.
Life like (Walthers owned) Proto 1000 or Proto 2000 their top of the line some of the early Protos are prone to splitting drive gears otherwise good quiet runners, early run steamers (Proto 2000) are weak slippery pullers, newr run steamers can be had with sound and traction tires ( I don’t mind them others can’t stand them).
BLI/Precision Craft- well detailed steamers with factory sound, good running and sound runners that usually can pull a respectable sized train, traction tires or non traction tired drivers are often included with the locomotive.
Bachmann Spectrum is the top of the line for Bachmann -well detailed,smooth quiet runners, decent pullers, no sound, DCC ready, newer runs are offering factory sound systems (mine are the earlier non sound versions).
Those are my picks from my experiences with these brands respectively.