Scale Railroad: Code 100 Shinorhora/Scenery Unlimited flex and turnouts, with a couple of Old Pullman's in the mix.
When I used to modulate: AM Flex
On the Carpet: SHS S-Trax.
I used some K-Line S track for a while when I first got sucked into the Flyer Dimension, but the end of the rails were poorly trimmed and the rails loaded up with crud quickly. It wasn't as good as their 3-rail O gauge track.
Rusty