The best: 3-rail O-gauge still allows for ultra-simple track wiring (no such thing as reverse loops, or wyes, in an electrical sense).
The worst: 1-1/4" track gauge in O-gauge means .073" (approx. 1/16") too wide for 1/48 scale fidelity - Heresy, by God! (The world is coming to an end - arghhhh!!!!).
Fortunately, as much as I like scale and prototype fidelity (), I think I can still live with 3-rail and 1-1/4" gauge as far as O-gauge is concerned, thank goodness.