I once raced my daughter back from LHR to SW3, with her using HEX and me the tube and both using public transport and walking only. Neither of us had any noticeable delays. I beat her by just under 15 minutes, I only had one change (tube to bus) whereas she had two (train to tube to bus) and I spent a fraction of what she spent. Of course it would be different if we lived above Paddington station, but then that's not a fair comparison.

Equally, from my wife's office in The Strand, it's usually quicker by Tube than schlepping across London to Paddington.