[lmm]

It's not a short time because the train's fast, it's short because it's not very far. And the claimed speed advantage is based on a somewhat gerrymandered definition of "central london".

The express is sometimes worth it, but it very much depends on where you're going; the express simply dumps you out at Paddington which does not have great onward connections. Whereas the Piccadilly line, being a tube line that goes right through the centre, can often take you directly where you want to go (particularly as a tourist) - Piccadilly itself, Leicester Square, Covent Garden, Kings Cross, ...

[Nrsolis]

None of this matters much to me since I'm often staying someplace close to Paddington and/or Mayfair. If I'm not staying there, I'm off to Canary Wharf and it's a taxi ride no matter what.

If you're fine with lugging baggage up and down the tube stairwells, then fine by you, but I prefer the Express for any number of reasons and time of travel/distance traveled isn't the sole determinant of my choice.

[lmm]

If you're staying near Paddington then sure, it makes sense. But for going to Canary Wharf the tube option is pretty nice - just change at Green Park (step-free since the rebuild) to the Jubilee line.