Joe 1.20.3 quite frankly, is HUGE, and unless the area the layout is also HUGE, then it can look very cramped if its squeezed into a small space.
My indoor layouts have all been built to 1/22.5, because there is a lot of stuff in those scale available on the market and it looks and works well in a constricted area.
1/20.3 is much larger, when you see a Bachmann K-27 with a couple of Accucraft 1/20 coaches you kinda have to tell yourself its not “ride-on” scale, but its flipping close to.
Also 1/20 stuff out there now K-27, C-16, anything from Accucraft, all have a MINIMUM curvature of 8’, but most require 10’-12’ to work trouble free and up to 20’ to look "prototypical’, thats a heckova lot of real estate to find for anything other than a basic circle. Unless you have a spare cornfield with SUV size turnaround space, your layout is going to be limited. At least with 1/22.5 curvatures using 6.5’ or even 8’ are easier to incorporate.
So, it really all depends on what rolling stock you REALLY REALLY want, if you will just die without a K and some J&S coaches then 1/20 is your choice, but if you find an Annie and a string of Bmann coaches have the right appeal, then 1/22.5 it is.
Personally, just ME speaking, if I had the real estate in my yard, I would still go 1/22.5, its just alot easier to live with.