I’ll be using the line tomorrow from Liverpool Street, travelling on to Oxford. GWR journey planner suggests is aware of the Elizabeth Line and suggests I catch it - as far as Farringdon (2 minutes)- then change to the London Underground. I can’t see any scenario where this would be scheduled to be quicker In normal operation.
Having done both today, I’d suggest timings concourse to concourse for Liverpool Street to Paddington are very similar for both the H&C and Elizabeth lines. Liverpool Street EL is a good walk from the mainline concourse, contrasting to the ease of getting to the H&C platform.
Getting off at the Paddington end is much of a muchness - EL leads easily to the main concourse (platform one end) and the H&C leads to the over-bridge to all platforms. The main variable will be the train every five minutes turn up and go, vs the frequency of the H&C.
Having said the above… what I would not do is change modes at Farringdon!
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It was good to see the Elizabeth Line busy today - a good mix of people there for the fun of being there, but also people actually using it from A to B. I find it amazing how Londoner’s habits can be the same for years, but all so easily change. I used various services on and off between 1pm and 8pm.