wrote:

In a couple of weeks the Mrs. & I will be arriving at Heathrow T3 headed
for St. James Underground Station. Due to our Travelcards and railpasses,
taking LU all the way or taking the Heathrow Express to Paddington, then
LU to St. James would incur no additional cost to us.

What rail pass do you have? A Britrail? I wasn't aware they allowed travel
on the Heathrow Express, as the domestic equivalent (All Line Rail Rover)
doesn't.

The Journey Planner shows virtually identical travel times regardless of
routing. As we travel extremely light, luggage and stairs are not an
issue. Does anyone here have a preference? Or, assuming "good service"
reported by all affected lines should we simply go as the spirit moves us.
We have ridden both services downtown before, so we are familiar with each
experience, however never really paid attention to the timing or ease of
connecting. Thanks.

Without heavy luggage, I would probably opt for Heathrow Express, then
Circle Line for St James's Park. If you take LU all the way, Barons Court is
a good place to change from the Picc to the District line, as it's
cross-platform. If you leave the change until Earls Court or South
Kensington, you will have to negotiate stairs/escalators for no time
benefit.

Chris