Some USA Trains is 1:24, the nicer stuff is 1:29
Piko is supposedly 1:29 in some cases, but there is some 1:32, and some goofy scaled stuff.
LGB is all over the map, mostly closer to 1:26
Piko quality ok, but not LGB level, hard to compare to USAT
No one makes the wide variety of USA diesel models that USAT does, so it depends more on what you want to model, USA or European, Steam or Diesel or Electric.
Overall quality ok, but not bulletproof like LGB.