My current layout uses HO Code 100 throughout, simply because that is what I started with years ago, and have utilize some of my original track and turnouts, including some brass flex and sectional in the yards! Mostly I have used Atlas turnouts, both Snap and CustomLine, as well as Peco and Shinohara, just depending on what I had on hand. Peco Code 100 is really OO and in a very few places, the gap between the stock rails and the guard rails is a bit too wide (fixed with plastic shims). Peco is handy because of the snap-over features...where I can reach them manually. Where remote is desired, I had to use some older switch machines with the snap springs removed. The Atlas turnouts are handy where the sub-layout framing prohibits under-the-surface switch machines. Were I to start from scratch nowadays, I would probably start with Cope 83, maybe using the new Walthers turnouts. One thing that is interesting, is some older Atlas double-slip turnouts I had, that worked great in a particular application. Unlike most double-slips, the Atlas align the points such that you cannot derail going through from the opposite direction. The routing will either be a crossing or a curved route. The switch machine is integral with the turnout. Too bad they aren't made anymore, nor in Code 100 and 83.