Model railroading isn't like a game console. You don't have to chose between compatable systems and then buy only things made for that system.
HO (and every other size) is a scale, that is, a proportional (in this case, 1/87th) representation of the real thing. Everything sold as HO scale should be manufactured to standards, and should be compatible together, within reason.
Now, this isn't totally true. Different codes of track require some effort to join, different brands of "roadbed" track need some major surgery to join to other brands, and some longer equipment won't operate properly on tight curves and turnouts, but in general, just because you have Bachmann, or Kato, or Atlas, or whatever track doesn't mean you can't run locos and cars from other manufacturers on it, nor does it mean you have to get a DCC system, or decoders, made by that same company (for DCC, the power supply, base station, and throttles must be from the same company, but decoders, circuit breakers, boosters, reverse loop controllers etc., don't have to be).
I have track pieces from MicroEngineering, Atlas, and Walthers on my layout, and locos / rolling stock from Atlas, Accurail, Athearn, Bachmann, Bowser, Exactrail, IHC / Mehano, Rapido, Stewart, and Walthers (and probably some others that I'm forgetting). If you add roadbed, structures, non-train vehicles, and scenery materials, the list of what I am using grows exponentially. All of it in HO scale and all of it interoperable.
