Never driven a diesel vRS but in terms of ST TDCI vs petrol vRS, the Octavia p*sses all over the Mondeo in every way I can think of. Apart from fuel economy – that was excellent in the Mondeo.
Another plus side I forgot to mention, when your Mondeo does go wrong, you may have to deal with the local Ford dealership which if they’re anything like the ones in and around Halifax/Huddersfield/Bradford, is marginally more painful than slowly pushing a javelin through one ear and out the other whilst drinking Fosters.
My only knowledge of the local Skoda dealers was when we were looking at getting a Fabia vRS a few years back who bent over backwards to try and find the right car for us. Not had go anywhere near a garage with the Octy yet in nearly a year of ownership.