"Old" Flesichmann (with the 3-pole motor) will run forever with no more attention required than an occasional oil/clean & carbon brushes.
"Old" Roco - either a good one or a bad one, running wise.
"Old" Piko - avoid locomotives - some rolling stock good but it depended on what factory made it (East German was a sort of co-operative).
New Piko is generally good - however, IMHO the differences between Hobby, Expert & such do not always make sense.
Brawa is nice but delicate, not very good on replacements parts.
Hornby Rivarossi/Jouef/Lima is good - some of the last products from this group before Hornby are also good.
Spares for Fleischmann/Roco & Piko are pretty good for models under 10 years old.
Some of the smaller manufactures produce some nice (& sometimes rare) models, such as LS Models, Acme, Hobbytrade.
Comments based on my own experience.