Commuters: Cheapest train line to live on

[Sublime66]

Wondering if anyone knows which train line is cheapest between West Country and London. Is it the Great Western line from Bristol via Westbury, Reading to London (this line seems to very fast). Or is it the South Western line that runs Yeovil, Salisbury Woking to London (slower)?

I know South Western falls into the Network Railcard area giving 30% off but am wondering which is cheaper full price mainly.

thank you

surely it depends where you are starting from - Bristol & Yeovil are over 40 miles apart?

Yes obviously it depends where you start from. Im not talking about Bristol vs Yeovil to London, I’m talking about in general which train line is cheaper when considering similar distances.