The Bachmann sets tend to be on the cheaply made side. Often to add more accessories they will cut corners on the loco. Several of their kit locos are run with pancake type motors that are less efficient. Also their gearing is not as refined. The Bachmann kit series cars tend to be lighter and for this reason derail easier.
Atlas makes a good locomotive. I also prefer their cars over Bachmann.
Have you considered Athern? There locomotives and cars are well made.
I would stay away from the entry level Life Like and Model Power sets as they tend to be of lower quality than the Bachmann.
Bachmann's Spectrum brand is a different consideration though. It should not be confused with their base line. Spectrum items are of high quality.