I have two layouts. The 12'-by-8' has an O-72 loop and siding on which I run the larger engines and passenger trains. My most recent purchase was an MTH Premier Boston & Albany Hudson that is so nice, I may never take it off the layout. The middle loop is O-54 with a passing siding and those tracks get the first-generation diesel engines, small steam and freight trains. The O-36 inside loop was added last and usually gets a diesel switcher and a short freight. The 10'-by-5' layout is just a loop of O-54 on which I run smaller engines, a few passenger cars and short freights. All track Atlas O. There's never enough room...
MELGAR