Not brand loyal. Hi-Railer, modern stuff, a few older pieces for grins (I have a little Lionel 2-6-4 221 "collection").
I run TMCC and descendants, so the MTH locos are always second choice if Lionel and/or Friends also offer it. I like MTH stuff very much, as models. I have all brands; 3rd Rail and Wms are my least-owned of the in-business majors.
Rolling stock? Any good piece, but it always seems that MTH makes the nicest stuff. K-Line die-cast cars still make me look.