I have been into N-scale for a long time, but have been taking up a larger interest in O-gauge the last 4 or 5 years. I'm not fussy, I collect any affordable and decent quality brands that offers trains in pre-bankruptcy blue "Rock Island" schemes.
Scale or plausible only, no fantasy R.I. paint schemes.
I find it a little too limiting (okay, maybe WAY too limiting) to just collect a particular brand name or two.
Heck with that.