Welcome to the Forum!
To answer, Track that fits your engine. Big engine,large radius curves. O or o27?
O27 curves won't help if the engine needs 31 inch radius curves or more.
I use old tubular O and O27. I have switches in both scales. Bought them by the box. The track is easy to fit custom because all you do is cut.
I do table top and change to my whim.
For a layout you need to plan for a more permanent situation.
Fast track is fast and easy and locks.
Gargraves has a fancy look with a thin center rail.
Other track is available.
What's available,cost, and personal preference.
You need to expand on the last one.