16 or 14 gauge wire

Larger wire means less resistance and less voltage drop. Look at Lionel's recommendation being the minimum size, but going a little larger is beneficial.

It also depends on what you want to run too. Postwar locomotives, with their dual universal AC motors and incandescent bulb lit passenger cars can pull a large amount of current. More current means more voltage drop. On the other hand, if you run modern era locomotives with their can motors, there will be less current. I agree with BMORAN4 above. Install the larger wire up front. That way, if you want to run a big power hog engine sometime in the future, you can.

Use 14 gauge.

Done.

If you are going to run DCS, run 14 ga. stranded to you distribution point anf

d 14 ga. stranded to the track.  See Barry's book, it is explained there.  Also, stranded because the DCS signal travels on the outside surface of the wires.  You get better signal going to the rails.  Also, isolate your center rail into segments of about 12-18 feet each segment.  The outside rail can remain one section but run wires the same as center rail.

Bruce

I used the star wiring method for my layout and I chose 14 gauge wire for the reasons others have mentioned above. I run the 14 gauge wire straight to the track from the distribution point and do not have separate drops.

I would also recommend using paired wire if you are going to add DCS in the future. This is the type of wire that is recommended in Barry's book for the best DCS signal.

Thanks for the quick responses. Looks like 14 gauge it is.

I have a good size Legacy layout and run 16 ga with no problems. Could be because all my engines utilize odyssey or cruise so I’m not seeing voltage drops. Since your just starting, take Rich’s advise and go with 14 ga. That way you’ll be ready for anything that comes you way.