Given that you are restricted to a 4 x 1 base board you ought to be looking at the length points for each scale, combined with what you want to achieve.
You would be able to achieve an inglenook style layout in all three scales.
Would your stock use commercial couplings as fitted or will you be using the buffers as per the prototype for propelling moves?
What size locos would you want to use? That length plus a couple of wagons will dictate where your first point would be placed.
Have a look at Ian Rice's and James Hillton's books on small layout designs.